Check for spam pages, cloaked pages, pages you don't know about.

Examine site for things martinibuster suggested for insight as to what happened. If not able to do that simply, restore an older, known to be clean backup of the site (after deleting all files on site first). Time consuming, but put you back where you were.

You do back up your site? (Hope you did!)

I didn't know people still used Dr. DOS? I think you mean DDOS ;)

Sorry, had to chuckle at that one ;)

Are you signed up with Google's Webmaster Tools? They have a message center in there to alert webmasters for potential problems they may have identified.

Sounds like you may have been hacked. Search your source code and see if anything is out of place.

Yes DDOS attack, sorry

There is no change in files, this attack cacth same time gg bot spider, more then 10000 differents ip.
Server stoped with overload.
no changes in urls, no changes in site after.

urls with problems are the same google bot try cacth during attack time.

Check server to exploits, nothing found.
Try new channel, new ad code, no results.
After 5 days a few number os urls with problems are fine now.
Site have more then 900.000 urls, half have this issue.
Contact with my adsense account manager, he send issue to adsense thecnical support, i haven't answers yet.

Revenue and CTR drop +/- 50%.
To be sure, after attack i restore a backup, no results.

Webmastertools don't report any issue with site,

Sorry my bad english

You may just need to wait for what's in Google's cache to work its way back out.

Seems gzip compressed HTML wich Media Bot can't process.
Normal SERPS have fresh results for this URLS.

I rebuild apache, turn off zend, i alls have Gzip on this server, some corrupt file ? i don't know....
I have more sites with it in same server 4 more, no problems at all.

I'll report later if issue is solved or not.

Thanks

Almost solved, 99% of site seems normal, revenue back to normal values.
Only a few deep links haven't relevant ads yet.