In order to get round the above, I copied the RDC application and put it on the desktop and renamed it to something like "Remote Desktop Connection 2". If you open the orginal (in your applications folder) it opens. Then connect to your remote computer. Fine, works. Open up the the copy on your desktop and it opens too. Again, connect to your second remote machine. It works. I managed two simultaneous remote sessions, across a VPN to my office.