Replying to theget:
Problem found, the plugin looks for "priority" what we don't have in our trac.
Thanks for posting what you found. Since Priority is a default field in Trac, the original developer probably considered it a safe assumption that the field exists. However, we should be checking that it exists, and creating a patch should be fairly straightforward.
Looking at the source code just now, I see that priority is being selected in the query but don't see a place that it is being used, so the fix may be very easy to do.