After more procedures on that server, we discovered, at least we thought, that most of the related problems were in fact related to a major crash at the network share drive level which occured in the last two days. So, full restore of the servers were done. Then, suddenly, out of nowhere, this problem was gone. I did about 200 hits to the server. I thought it was resolved and related to the problem which was restored. Well, it started to do that again. I had it once after 200 hits. Then, since then, it is working ok. This is very strange. When it happens, IIS cannot get a hook on it.

Anyone had some kind of behavior like that with IIS that after a while the same images become unavailable as if something is locking them or not releasing them once accessed?