Reason #1: You’re using frames.
Many search engines have problems with frames. They often only index the frameset page and not the individual frames that contain the actual content. Unfortunately, the frameset page usually doesn't have META tags, title and enough content (text) to obtain a listing on a search engine.

The best solution to this problem would be to avoid frames.

Reason #2: Your Web site has a low link popularity.

This is huge with the search engines these days but I see very few people are going about this the right way.

I wrote an article on proper web linking based upon my research and experience.

Basically link popularity are other sites linking to you. And there are some very important factors to consider here.

• Quality is always better than quantity.
  
• And link relevance / reputation is always important.
  

Free Link check program.
http://www.checkyourlinkpopularity.com/

Reason #3: Your Web page URL contains special characters.

Most search engines have problems indexing Web pages when their URLs contain special characters. The following special characters are known to be "search-engine-spider-stoppers":

* ampersand (&)

* dollar sign ($)

* equals sign (=)

* percent sign (%)

* question mark (?)

These are usually characteristics of dynamic pages – Goggle will index one level down.

Reason #4: Your Web pages are created dynamically.

Databases and dynamically generated Web pages are great tools to manage the contents of big Web sites. Imagine you'd have to manage the Web site contents of a big newspaper without databases...

Unfortunately, dynamically generated Web pages can be a nightmare for search engine spiders because the pages don't actually exist until they are requested. A search engine spider is not going to be able to select all necessary variables on the submit page.

The exceptions are the spider programs from Google and Inktomi. They are able to index Web pages that are dynamically generated, even those that use question marks and query strings.

Reason #5: You are hosting your Web site at a free Web space provider.

Some search engines (e.g. AltaVista) limit the number of pages they will index from a single domain. For example, if your Web page is hosted at Geocities.com or Tripod.com, it might happen that your Web site is not listed just because the maximum page limit for that special domain name is reached.

Some search engines no longer even index pages residing on common free Web hosting services. Their complaint is that they get too many spam or low-quality submissions from free Web site domains.

However, Google is the exception. Google does index Web pages on Geocities.com and Tripod.com.

Reason #6: Your host server was down or non-operational during spidering.

It can happen that your Web server is down when a search engine spider tries to index it.

If your Web site fails to respond when the search engine spider visits your site, your site will not be indexed. Even worse, if your Web site is already indexed and the search engine spider finds that your site is down, you could be removed from the search engine database.

It's essential to have Web space on servers that are very seldom down. Choosing a reliable Web space provider is very important for a successful online business.

Even someone you promises 99% up time means your business would be down 4 days during the year – so pick a reliable host. And then monitor it – there are some programs you can use for that.

Free monitoring service:

http://www.internetseer.com

Reason #7: Your Web site has a slow host server.

Search engine crawler programs that index Web pages don't have much time. There are approximately 2-4 billion Web pages all over the world and search engines want to index all of them.

AltaVista and Google specifically mention the problem on their Web sites.

AltaVista: "If a site has a slow connection or the pages are very complex, it might time out before the crawler can index all the text."

Google: "Your site may not have been reachable when we tried to crawl it because of network or hosting problems. When this happens, we retry multiple times, but if the site cannot be crawled, it will not be listed in our current index."

Reason #8: Do you use the right keywords?

It's important that you use the keywords on which you want to be found in the right places on your Web pages.

And also some keywords will sell better than other – it’s all based on properly targeting your market.

This all is a part of the initial planning and targeting phase, which I contend, is critically important.

You may also want to limit the size of your homepage to less than 60K.

Reason #9: You are using a lot of images on your Web site but very little text.

Your website reputation is based on text and not pictures.

Search engines need text to index your Web site. They cannot know what's written on your GIF or JPEG images. If you use a lot of images on your Web site, you should also create some Web pages that have a lot of text.

Some Web site promotion consultants will tell you to create so-called doorway pages. For those not familiar a doorway page is a Web page that contains plain text and a link to your main Web page. On that doorway page, you should describe the content of your Web site in many sentences that contain many keywords that are important for establishing the reputation of your Web site.

However, some search engines only lists Web pages if at least one remote Web page is linking to it. In that case, a doorway page will not work. In other words a doorway page that just stands alone won’t work today especially with Google – they used to but not anymore.

Don't use doorway pages for search engine spamming! Only use doorways that have something to do with the content of your Web pages.

Of course content is ultra important and I can give tips on some ways to get or generate content.

One way is something called a blog.

Reason #10: The submitted Web page is only a redirection.

Note: Since this was written several years ago I have noticed that redirected pages are showing up in Google. At this point in time your main reason for redirecting would be where you have multiple domain names and you're redirecting them all to your main site to eliminate duplicate content penalities.

If the Web page you submit contains a redirection to another Web site, most search engines will skip your Web site completely. Do not submit a redirection Web page. Webmasters tried to put one over on the search engines in the past, the search engines caught on and stopped this practice.

Of course their can be legitimate reasons to redirect your pages, like you moved some pages to a new domain.

One way of dealing with this is using the META Refresh tag on the old Web page, for example <META HTTP-EQUIV=Refresh CONTENT="4; URL=http://www.lifeplusvitamins.com"> tells the browser to load www.lifeplusvitamins.com 4 seconds after the current document has finished loading. However, some old Web browsers don't support that tag, and some search engines penalize pages that use a refresh of a few seconds or less. In other words if it’s too quick they think you might be just trying to trick them – being the search engine.

Instead of the META Refresh tag, another method is use JavaScript to load a new document:

<SCRIPT LANGUAGE="JavaScript">
<!--location.replace("http://www.your-new-site.com");

--></SCRIPT>

Most search engine robots ignore JavaScript so this method of redirection is unlikely to be penalized

Reason #11: You have submitted your Web site too often.

If you submit your Web site more often than once a month, most search engines will consider that spamming and they will skip your site.

Spamming does not work with search engines. Most likely, it will backfire on you. More and more search engines are able to detect spam attempts and penalize or ban your page from their listings.

Remember the purpose of the search engine – they are in business to make money – not to be your good buddy and list every page you throw at them.

Here’s a little known but extremely important tip concerning Google- if the page you submit does not have another page in the Google index linking to it – Google ain’t going to list it if you submit it 100 times.

Reason #12: You overuse keywords on your Web site.

Many search engines fear to be spammed if you overuse keywords on your Web site. Do not repeat your keywords too often in your meta tags or in the body of your Web pages.

Nobody knows the magic number because it can vary based upon the search area and other factors but there are certain percentages that the search engines like for optimal results. For example a paragraph such as the one below is not a good idea:

Bob’s Water Heater Page

We have water heaters for grandmas

We have water heaters for grandpas

We have water heaters for girls named sue

We have water heaters for boys named blue

We have water heaters for guys named Sam

We have so many water heaters I don’t give a flip.

Reason #13: Hidden Text Trick in the background color of the web

This is an old trick and there are variations – I used to use this and there are still ways to get away with this but you need to be very careful. Also you can inadvertently hurt yourself unintentionally.

For example, suppose you have a Web page with a black background and a table in that page with a white background. Now suppose that you've added some black text in that table. This text will be visible to your human visitors, so in fact, the text isn't hidden. However, the

search engines can interpret this to be hidden text because they overlook the table background color.

Reason #14: Your Web page does not have unique IP address.

Does your Web site have a unique IP address? If not, your Web site is running the risk of getting banned from the search engines.

Human beings use domain names like yahoo.com, but network computers use IP addresses, which are numeric addresses written as four numbers, separated by periods.

Every domain name translates to a so-called IP address..

Many Web hosting services don't give out unique IP addresses to their customers to save money. They assign the same IP address to multiple domain names. This means that a number of Web sites could all be using the same IP address as your site does.

Reason #15: You don't allow robots to index your Web site.

Robots.txt

The host server might have a plain text file named "robots.txt" in the root directory. It contains rules for the search engine spiders.

The syntax could basically be wrong - here is a free syntax checker

http://www.sxw.org.uk/computing/robots/check.html

And I could certainly look at any specific situations.

META ROBOTS tag. If you find the following HTML tag in your Web pages:

---

<META NAME="robots" CONTENT="noindex,nofollow">

---

you should replace it immediately with

<META NAME="robots" CONTENT"="index,follow">

Reason #16: Your Web pages require a full-fledged browser.

Basically if your Web pages require Flash, DHTML, cookies, JavaScript, Java or passwords to access the page, then search engine spiders might not be able to index your Web site.

Reason #17: Search engines could not resolve your DNS name.

It takes approximately 2-4 days until a domain name becomes active. All Internet access providers must update their records (DNS tables) to reflect new site locations. The process of updating DNS tables is called propagation.

So the bottom line is you need to wait several days after hosting a domain name to submit it to the search engines.

There is a text-only browser named Lynx you can download and test any pages you have a question about.

http://www.delorie.com/web/lynxview.html