I'm having some similar problems with my 128 meg muvo.
If i'm copying mp3s to it, it'll be fine, and I'll be able to put 122 meg of mp3s on there without a problem.
I wanted a bit more music on there, so I re-encoded a bunch of songs as 64kbit wma files and tried to copy them on.. I can seem to fit only about 93 meg of wma's on here before it comes up saying the disk is full. It will usually let me create an empty text document at this point, and I kept adding to it until it was a 20 meg txt file without a problem. But if I delete this 20 meg text file and try and copy a 500k wma file on it, it'll still come up saying that the disk is full.
There are currently 63 files on the player, including settings.dat.
The player is formatted as fat16 using the utility that comes with it on the cd. Should it be formatted at fat16 or fat12?
I had the problem where the player wouldn't turn on the other day too. If I deleted all of the items from the player using windows explorer, it would show as being empty, but if I removed and plugged the drive in again, it would show up with 2 or 3 wma files that I had previously copied, but with a 0k file size. After I formatted it using the creative utility it turned on again, but it's still having these disk space problems with wma files.