Fantastic! I'm so glad to hear your sleuthing uncovered a few things and that the JoomBah system plugin you had to disable wasn't critical for your needs. Very strange indeed, but as long as it's working, I'm not going to investigate further.
As for authentication, it sounds like LinkedIn is working.. sweet! Are you still having issues with Twitter? If so, let us know what they are and we'll get that last bit knocked out for you.
Thanks,
Alex