I decided to replace my mower blade drive belt. I thought it went OK but after everything was put back together the mower will not move. When running I put it into gear but nothing happens and when it is turned off and I put the "freewheel" in the engaged position, it will not move.

Hi,
You have one too many numbers in that model number.
Park brake locked? Blade belt should not affect motion drive.
Peace,
Clarke

The model number in my question is exactly as it is on the owners manual. The aprk break does not appear to be locked. THe parking break level changes position to lock it and unlock it.

I have to agree with Clarke on this. Based on our experience a Craftsman tractor has 6 digits in the model number to the right of 917. XXXXXX http://www.managemyhome.com/mmh/owner_manuals When you replaced the belt to the deck you would not need to touch the drive belt, or did you?

Please Google the sears number 917.2720601
And you will see it is the number. I do not know a lot about these numbers, you folks know a lot more about these things than I do, but it is the number sears has assigned to this model tractor.

I am very surprised since I never saw a serial number long before. Have you checked that drive belt yet mentioned in post #4?