I had this problem and I found a solution that is not a good solution but it works. I set up a "fake" gmail account for each of the players who didn't accept my invitation to join. Then, I invited each player to join using his new "fake" gmail account. Then, I logged onto each new gmail account to accept each invitation on behalf of each player. This is a bit of work to set up but it works fine once it is set up.
I had this problem and I found a solution that is not a good solution but it works. I set up a "fake" gmail account for each of the players who didn't accept my invitation to join. Then, I invited each player to join using his new "fake" gmail account. Then, I logged onto each new gmail account to accept each invitation on behalf of each player. This is a bit of work to set up but it works fine once it is set up.