Strangely, last night I had a similar error but with a different code (it started with 0800, I can't remember the rest of it.) I think it said "synchronise failed while checking media" instead of download failed. Anyway the "Synchronising" display on the Empeg was frozen (not moving around as it usually does) and the whole thing was locked. I gave it ten minutes in the hopes that disk caches would empty and such, and pulled the plug. I retried my sync, the file system check went okay, and I haven't seen any ill effects so far.

I would try to drop to a shell (assuming you have the developer version installed) and see if you've got your FID files out there. If so, I think you might be able to connect via Emplode, and I think it tries to check the database integrity when it connects. It should detect that something is out of wack and try to rebuild the database (I think.)

Wait for one of the Empeg guys to give you more solid advice, though... 80 gigs is too much to lose.