I got the same thing last night for a domain that has been deindexed by google for over a year. I took out all the ads right away. I hope thats enough until I can fix whats wrong. I just wish they were a little more specific on what the actual problem is instead of being so cryptic.
Being cryptic is what they seem to be best at. I got similar messages in January. I kept asking what the problem was - they just pointed to the TOS without any other information. Google disabled ad serving from any sites they did not like and that was the end of it. A third of my "empire" became worthless overnight.