I have looked in a few places, and have found some of the most common errors when using Google Adsense. Most of these errors will get your account permanently banned by Google. I tried a couple of them early on not knowing what would happen, but Google graciously sent me a warning e-mail to stop fraudulent activity, so I stopped and have not had any problems since.

All the links to the original articles are included.

1. Clicking ads on your site.
This is the biggest of all the adsense mistakes and an easiest way to get your account banned.

2. Editing adsense codes.
You are not allowed to edit the adsense codes you obtain from your adsense account. It is also advised to make the color changes etc from the adsense account itself instead of editing it from the codes. This is to avoid the possibility of mistakes.

3. Placing more ad units than allowed on a page.
Only 3 ad units, 1 link unit, 2 search tabs, 4 different referral buttons are allowed on a single page. It should always be made sure that all your pages are within the allowed list.

4. Using other contextual PPC ads together with google ads.
You are not allowed to display other contextual ads on a page which is showing google ads. Google ads, YPN adsc etc. are examples of contextual ads. Amazon ads are examples of non contextual ads. However there is a debate on whether amazon’s omakase is contextual or not. It has been informed by adsense support that Amazon ads can be displayed on the same page with google ads.

5. Labeling ads with texts other than “sponsored links” or “advertisements”.
Only the above mentioned two labels are allowed for google ads.

6. Disclosing your adsense reports data to public.
You are not allowed to disclose anything other than your aggregate earnings to others.

7.Placing direct download links for music or video on your adsense site.
According to adsense TOS, no link on your site should directly lead to audio or video result.

8. Not blending ads with your pages.
To get a good click through you should make ads look like a part of your site.

9. Setting up the payment hold for too long.
Adsense is very strict about click fraud and they can ban any account if they detects fraud clicks. Once you are banned they won’t pay you the money you earned before you were banned.

10. Not checking your adsense reports at least once a day.
If you don’t check your reports regularly you won’t know when something suspicious happens on your account. If you are checking it regularly you can write to adsense support whenever you find something suspicious and it can save your account from getting banned.

11. Not reading adsense TOS and PP carefully.

12.Creating more than one account.

13.Placing ads on pages with no content.

14.Masking ad elements.

15.Sending your ads in html formatted emails.

16.Referring people to visit search results page from your adsense search tab.

17.Placing ads on a site in unsupported language.

18.Specifying google ads as alternate ads.

19.Not adding spacers or boarders to seperate ads from images.

20.Getting into the clickgroups.

21.Placing your ads on sites created just to display ads.

22.Placing too many ads and keyword stuffing.

23.Launching a New Page for clicked ads by default.

http://brokencodes.blogspot.com/2006/09/13-adsense-mistakes.html

24. Do not alter the results after ad clicks or searches - Ensure you are not in any way altering the site which the user reaches to after clicking the ads. Do not frame, minimize, remove, redirect or otherwise inhibit the full and complete display of any Advertiser Page or Search Results Page after the user clicks on any Ad or Search results.

25. Ensure you Language is Supported - Adsense supports “Chinese (simplified), Japanese, Danish, Korean, Dutch, Norwegian, English, Polish, Finnish, Portuguese, French, Russian, German, Spanish, Hungarian, Swedish, Italian and Turkish”. In addition, AdSense for search is available in Czech, Slovak, and Traditional Chinese. If your web pages language is not supported, do not use the code on such pages.

http://www.quickonlinetips.com/archives/2005/05/15-common-mistakes-by-google-adsense-publishers/