My apologies to Bruce and to everyone else who replied to my request for help. Unforeseen circumstances have kept me off of groups.io for a couple of weeks and I'm just getting back to it.
Bruce: I don't know for sure that your "wild guess" was correct, but your solution sure was. When I typed in the invitee's email address instead of pasting it, the invitation was sent, she received it and we were back on track. That still doesn't help me understand what "Failed - force failed" means, but as long as the invitation went out, I'm not sure I care enough anymore.
To reply to Willow Raven, there was no number for the error message. "Failed - force failed" was listed in the Status field of the Sent Invitations page, where I normally see "Accepted", "Sent" or "Sent - Expired".
In any case, thanks to everyone who replied and, again, my apologies for the delay in getting back to you.
