Small Engines (Lawn Mowers, etc.): Lawn mower doesnt move when in gear, speed transaxle, lawn tractor

Question
QUESTION: I have an Craftsman 42" 6 speed transaxle lawn tractor. When I put it in gear, it doesn't move. The drive belt is ok. the clutch/brake pedal is moving all the way back to transmission. Even with lawn mower is turned off, and mower is in gear, I can push mower like it is still in neutral. Any ideas?

ANSWER: What is the mower model number so I can look up your transmission.  The model number format is xxx.xxxxx

Let me know the model number.
Eric

---------- FOLLOW-UP ----------

QUESTION: The model number is 917.27071

Answer
If you lift/jack the rear of the mower up can you turn the wheels by hand?  

Did the problem occur suddenly or has the mower sat a while?
Is the brake stuck causing the transmission not to turn?  The brake is a small disc located on the side of the transmission.
Let me know.
Eric