Can't delete invitation to Email

Can't delete invitation to Email

I'm having trouble adding a new user in our control panel for morrispaint.com. I am trying to add chad.simmons@morrispaint.com but I keep seeing a red error that flashes by so fast I can't read it and the user is not added. It seems that the user is showing up in the Invited Users list for some reason. I've deleted the user from the list several times now, but it keeps coming back and I cannot add the user do to this.