After upgrade to 6 dongle fails on version 4

I upgraded from Cubase 4 to Cubase 6 and installed it on my new Windows 7 machine. It appears to work. Now, when I used the dongle on my laptop with Cubase 4 to record, the dongle is no longer recognized.

What do I do to be able to continue with version 4 on the laptop (windows XP) and also have version 6 work on the windows 7 machine?

Thanks for any advice on solving this problem.