Also, sometimes you will get the Yahoo "purple banner of death" even when the invitation went through. Best to attempt to invite two people...one with an address you can check afterward. Sometimes doing a hard refresh (ctrl-F5) beforehand will help it go through, too.
One thing about Y!G...you can never be sure what's going on, and if there's anyone on the other end they seem to spend a lot of time asleep at the switch. Good luck!
Bruce
Bruce Bowman