hey there Bruce,
I also bought Qurb a long while back and it has worked fairly well for me. I do remember a time where it just stopped blocking any spam. I think I did a search on google for the issue and somehow came across a solution that actually worked for me. Someone mentioned that my Approved Senders list got too big and that was causing an issue (bug I guess?)... I deleted a bunch of emails in that list that I never get emails from, and everything has worked since.
It does seem like a really bad issue to have (we should be able to have as many on that list as we want)... but it did help at the time.
Not sure if this will help out, or if you have a completely different issue, but I hope it helps!