It happens on servers that are VAC protected, I was able to play on a server without getting that error and it wasn't VAC protected, all the other servers that were would give me that error, so maybe VAC is having a problem.
accusations to actual hackers is 50000:1.
Looks like Valve finally fixed the problem, yesterday I played on WNx Chicago server and today I tried others like 1138, all of them worked.