If you are receiving this message at Sedo it is usually one of two things,
1. Sedo has suspended your domain names.
2. Google has banned your names and therefore Sedo took further action and disabled your account from being able to monetize any names.
Probably
#2. Google does make mistakes on identifying fraud. As you say, someone else can come across your domains, click on the ads enough times to the point that Google would ban the names and/or Sedo. Either way, there are parking companies like ours that not only pay more than Sedo if your names are not banned, but also do monetize those names that may be banned by Google.
I suggest you give us a try - Bodis.com, because we tend to make more than Sedo.
Also, run a few of your domains through our API located here:
https://api.bodis.com/domainclassification?domain=somedomain.com
Replace somedomain.com with your actual domain. If it is showing "primary" it means your names are not truly banned and Sedo is playing tricks on you, and if it is showing "secondary" then yes the big G banned those names. We monetize both anyhow it's just that one pays more than the other.