I have fitted a Pioneer 107 AKA superdrive to my MDD and its fine.
just checking a few things.
Did you replace the combo or is it fitted aswell as the combo?
have you checked in system profile under ATA to see if its there?
Is it set to master, slave or cable select. ( I would set it as master and the combo drive as slave).
in mine the superdrive is in the top set as master and the OE combo is in the lower bay set as slave, and i had to remove a metal blanking plate from the lower drive bay when fitting.
Hope I can help..