Back in the MC 9.1, 10 and 11 days, we used to see quite a lot of those .XXXX and .YYYY files. They were temp files, usually used by MC when writing tags to a file required that the entire file be re-written to accommodate the incoming tags. MJ should have cleaned those up after itself, but for some reason, did not. Perhaps, as Alex has suggested, a virus checker had locked the file preventing MJ from deleting them?
The only other thing I can think of is that you are running Media Center 14 build 14.0.96.
Build 14.0.140 is available for download on the
Media Center download page.
The absolute first thing you must do is download and install this release, then check to see if that on its own is enough to fix your problem. This build includes a fix for a problem with windows 7 that was caused by redirection to virtual folders when running with UAC enabled.
Posted on the 30th November 2009, build 106 contained the following:
2. Changed: Minor application manifest change that should disable any UAC redirection (and the problems associated with redirection).
I'm not sure if this is where your problem is coming from, but would seem to me like the best place to start.
Certainly, the first thing anyone from JRiver will ask you to do is to update your MC, so better for you if you've already done that.
You do not need to uninstall your current Media Center, simply download the upgrade and install it "over the top" of your existing installation.
Good luck,
regards,
marko.