I have to admit I have had this problem once. The fix was so easy I had to laugh at myself.
Stand behind the back of the tractor. You will see a small rod on the lower right side with a diagram next to it. The diagram shows that if you pull the rod out, (engaging it) it releases the transmisson belt, so you can push the tractor. When it is released, the transmission belt in engaged. That is the position it should be in. Give that a try.
If that isn't it, you may have an issue with the transmission belt itself. Good luck.
Jason, October 2009
