It can be quite a shock to see your high page rank site suddenly disappear from Google. Getting banned from Google can severely affect your site traffic and advertising earnings. Listed below are some excerpts from Matt Colyer at Search Engine Journal List for common reasons google may ban your site -

1. Duplicate Content – This is when multiple Web pages have the same content.

2. Cloaking – This is Web pages created just for search engines, where it delivers one version of a page to a Internet user and a different version to a search engine.

3. Hidden text or hidden links – This is text or a link that is invisible to the naked eye on a Web page, but are seen by spiders.

4) Keyword stuffing – Keyword Stuffing is when you load a Web page up with keywords in the Meta tags or on the Web page?s content.

5) Linking to bad neighborhoods - Bad neighborhoods are designed to increase your Web site?s ranking or is Web site?s using bad techniques to increase search engine ranking. You should not link to any Web page that uses bad techniques to increase ranking.

6) Buying links for Search engine ranking – This where a Web site owner buys links just to increase his or her ranking. This is also used to increase Page Rank.

7) Machine Generated Web sites – This is a site that generates hundreds of web pages that are basically the same page repeated hundreds or thousands of times, but with a few unique lines of text and unique title.

So keep in mind that you may not be doing any of these errors unknowingly on your part. One common error is when you rename and upload fresh pages, they may duplicate the content of the older page and may seem to Google as duplicating content. You may unknowingly be linking to sites which have tried to trick google and if google bans them, it might ban you too. So track your links and keep them fresh. Too muck keyword stuffing to drive ads or traffic may get penalized, so keep it within limits. Never hide text with the same colour as the background, Google is too smart for that.

Google brings a lot of traffic to any site and getting blocked by Google is a bad move as it is difficult to get back in!