1. Update moodleB (this won't fix this error, but you should do it anyway)
2. Check the keys on both moodles to make sure they both still trust each other.
You can see if they're communicating by loading the 'services' page for MoodleB on moodleA, and then going back to the summary page - if the 'last connected' time just updated, the sites can connect to each other, and trust each other.
If not, you might need to manually tell each site to trust the other again.
You can do by choosing networking/peers in the site admin block, choosing your peer-of-interest, and entering in the new public key from the other site.
... random hopefully-helpful thoughts end.