I feel guilty for waiting this long to report these problems, but I have tried just about every release, beta or official, after 6.40 and have had to to go back to 6.40 every time.
I am running Windows 7 Home premium 64-bit. For each release of 6.41 and 6.42, nbpro unexplainedly quits downloading after a few minutes. Curiously, the program then refuses to entirely close (although the UI appears to close). It won't even close after a "kill process" request in Process Explorer. Before reinstalling 6.40, I have had to reboot every time. When 6.40 is reinstalled, the downloads resume and go to completion.
Again, I apologize for waiting so long to report this!