Some readers doesn't properly recongnize multissesion dics.

For my part i have a pioneer dvd rom and a sony burner.
My dvd rom often recognizes only the first session.
My burner always recognizes the 2 sessions.
I am lucky.
In fact I saw 3 types of readers with multissesions discs :
The ones that read it perfectly (like my sony burner)
The ones that sometime see only one session.
The ones that always see 2 sessions but never backup it properly.
-> I have had a 50x reader that made too big images with discjuggler (80 or 90 minutes instead of 70-80).

So you may try to flash the firmware of your reader or burner.
(Nero CD-Recorder Firmware site : http://ahead.de/en/Firmware.htm)
Then if it doesn't change anything, buy another one.

Good luck.

Alucard