Are all the fields you have marked as required in Virtuemart also setup with a mapping in JFBConnect? With VM2, I didn't think it was required to have it setup like that, but it's a good test. With Community Builder, it's impossible to save users if required fields aren't filled out, so there are other extensions that are very picky about the user profile being complete.
If you un-mark all the fields in VM2 as required, does that fix the problem? We'll have to do more testing with required fields and how VM2 responds to those that aren't mapped (or have no data) to see if we can recreate the problem though. Your feedback will help us understand how best to test.
Thanks,
Alex