"error reading file" at opening and no instruments available

Whenever I open Musescore I get the following message:

error reading file /path to soundfont/ at line 1 column 1: error occurred while parsing element

I click the ok button, but can't create a new document because the instrument list is greyed out. I searched the forum for the same error message without finding anything that seemed to help me. I tried changing the soundfont in Edit -> Preferences from FluidR3_GM to TimGM6mb, but got the same error message after restarting musescore. So it doesn't seem likely that the soundfont files in themselves are corrupt.

I also tried stopping timidity with this command

sudo /etc/init.d/timidity stop

since I seem to recall having had problems before with timidity invisibly and jeleaously wanting to control what sounds i can use. But this didn't change anything either.

Also, Musescore hangs and needs to be forced to quit whenever I try to close it.

I'm using Musescore 1.0 in Ubuntu 10.04. Or rather, I'm trying, unsuccessfully...<:-) I will be very thankful for any help as I have no idea how to begin to guess where the problem lies.