Unable to remove old session from DP9.04 (upgraded from DP7.03)

I've recently upgraded to DP9.04 and i've tried to remove some old sessions, but when i do i just get a poop thatsays

0 of 1 session(s) successfully removed

i've tried making a test backup and removing that session and that works.

So is it because i've not run the migrate DCBF files after the upgrade to DP9.04 and these files were still in the old format?

Thanks