0áπ└â–Σ.apl at 3.5GB
at 3.7GB
That looks like filesystem corruption.
Run
scandisk to fix it. Check both the "Automatically fix filesystem errors" and "Scan for and attempt recovery of bad sectors" checkboxes.
Judging by the size of those files, a lot of the stuff you've put on there is now corrupted, so you will have to copy it back on again.
If this problem recurs, it's probably because of one of (in decreasing order of likeliness):
1. You're not "safely remove"-ing the iPod before unplugging it from your computer.
2. Your disk could be dying.
3. There's a bug in Rockbox causing it to corrupt your filesystem.