Since this is a known bug as Maestro Linden stated, I think it would be helpful if you could manage your groups from the web login at secondlife.com
That would save everybody a lot of time as people would be able to fix this themselves.
I have the same problem and I dont have access to the group from my alt. I wonder why they dont fix it, seems theres a lot of people having the invalid character issue. :manmad: