Did you do an you do an update to you system before you used the system?  You will have to to add all of the vehicles.  Now, because you have an older GM, chances are you will have to start moving up in model year to find the car.  It will work.  So for example, to use ABS on my 2000 Yukon, I have to grab the program not in the 2000 Yukon, but on a 2004 Yukon.

A little tip, re-format your card before you try and update it.  If you don't it won't work.  If you do, it will go as smooth as pie.