"please exit any running games or tools before attempting to verify your game cache" message repeated
So this is definitely caused by chatlogger++, I forgot that might cause it and went through a very long list with steam support including updating the bios, reinstalling steam, and on, before I tried disabling chatlogger++, and then the messages stopped appearing.
Took this a while ago, but that was in the span of a minute. http://i.imgur.com/E0ePq.jpg
It happens sporadic waves, where a bunch of them will pop up, and then there will be a while where none come up.
I am happy to provide any other data. I am using the newest version of chatlogger++, 1.2 Win7 ultimate fully updated 64 bit. Not in the steam beta