Another possible fix:
stop nepomuk
Remove the file
~/.kde/share/apps/nepomuk/repository/main/data/virtuosobackend/soprano-virtuoso.trx
restart nepomuk
It worked for me without data loss
--
Virtuoso 6.1 upgrade crashes nepomuk
https://bugs.launchpad.net/bugs/631102
You received this bug notifi
Also after a clean installation of ubuntu 10.4 I have the same problem.
However, when I remove the uid and gid tag of the fstab line it seems the
problem is solved.
And it seems that USB NTFS harddisks work fine.
--
New timestamp when copying to NTFS partition
https://bugs.launchpad.net/bugs/314