You need to make sure you are using Single Snaphot or Install Monitoring. It won't work with Multiple.
Also, you do need a file called isrepackager.ini in the same location as the repackager executable. This has to have the PIDKEY in it like this:
[GENERAL]
PIDKEY=AAAAAA-1111-1111111111
So, if this is an eval, you probably don't have a PIDKEY, so you may be out of luck.
Jenn