This just worked for me as well...
I am running 2.3.5 and the error seemed to come on slowly.
meaning that It manifested as my inability to access the cms admin. (however my site, mostly a blog worked fine.)
at first I was being logged out of the cms/admin after a soft time (it would then show this error, but a refresh would let me back to the login screen)
Finally, I can not reach the login screen at all, however the site still runs fine.
The edit listed above has given me access to the cms/admin again.
I just had this problem, and I used the fix described. However, it did turn out to be a symptom of a bigger problem, namely that I had got an incorrect include (I had accidentally named it .php instead of .ss).
Thought it worth mentioning for anyone else like me who had made that mistake ;-)