Problem starting a remote control session

I sent an email invitation to a person whose computer I need to control.   They get the email and click on the link provided and their computer goes thru an install.   They then get a dialog box that gives a session number and instructs them to wait until I join the session.   My question is how do I join the session.    Or even more basic; why should I even have to join the session if I am the one that initiated it?    Any guidance would be appreciated.