I don't know anything at all about MUFS, but you say that you changed DH0: to FFS, so I'm assuming you're using DH1: still with MUFS?
If MUFS is on the RDB (if that's how it works) then it is still active I believe, so could well be causing you trouble....
Like Zipper said, it's worth doing a Virus scan. I recommend VirusZ.
Also, this could be file system corruption I suppose.
In that case, drag your DH0: somewhere onto your DH1: to back it up, and then reformat DH0: and copy everything back again. Of course this would be the last resort.
To check that you are actually using FFS on DH0: just type in "version dh0:" at a shell, and it will tell you the filesystem in use.
