In the example below, I have opened the first RAR in the encrypted set and entered the password - unraring starts and completes successfully. I can do this with all complete downloads and then the problem is solved however this babysitting of the client is not required in v5 - it just sees the downloads as done but unextractable and carries on. Here is a screenshot of the current situation in case it helps:

I have already tried increasing the cache level in the .nbi file but even when set to 1000, all that happens is the cache takes a little longer to fill at which point everything still grinds to a halt. Any ideas? As I say, if I dump 6 and reinstall 5, the same download list continues through these problems without stalling.