Well... those things happen, but I'm afraid there wasn't any fix regarding this mysterious problem (or at least I don't know about it, which I probably would if it were the case). We haven't identified the problem yet - any attempts to simulate the behavior were unsuccessful so far.
So, either the change was caused by something very subtle and basically unrelated (the virus definitions have stopped/started scanning some file, which changed the timing of the boot just a bit, maybe caused two drivers or programs to be loaded in an opposite order, compared to the previous state... and the previously occurring conflict disappeared. If timing is the case, the problem can appear again any time, of course.) - or, some other program, maybe the one related to the conflict, has updated?
(Just to be sure - have you booted your machine before the problem disappeared, or are you saying that it started to work in the middle of a running Windows session?)
But, there's one interesting thing here... when you say that of course you received VPS updates. That means that at least avast! was able to write to the disk (which I wouldn't consider for granted in this strange state). Also, when you created the msinfo32 log - did you save the output on your disk, or somewhere else?
Basically, my question is what were the locations you were unable to write to - whether it was really everything, or just a specific drive, folder, maybe only when performed under a specific user account?
Regarding the operations - wasn't it maybe only rename/delete that was prevented, and creating new files might actually be possible? (I wouldn't rely e.g. on MS Office behavior - when saving a file there, it might actually first create a temporary file and then try to rename it).
Thanks.