Hi, I could be wrong, but I'm assuming this is the error that the new person is receiving when they click on the email invite?
If so, it is typically one of two things causing this error. 1) The person is currently logged into a Google Account that is different from the account you sent the invite. For example, you sent the invite to
JohnDoe@gmail.com but when the user clicks on the invite, he is currently logged into another gmail/google account, such as
JaneDoe@gmail.com. 2) You sent the invite to the user's email address, but that email address is not registered as a Google Account. This often happens when sent to a non-gmail account such as
JohnDoe@yahoo.com. The user will have to register that non-gmail account...