Small Engines (Lawn Mowers, etc.): Craftsman Transaxle spinning in two directions at the same time, transmission work, transaxle

Question
I have an older (2002) Craftsman LT 1000 Model 917.271826 that I have been having issues with.  It seems like it was hard to get in gear and had power issues, so I replaced the drive belt.  After I got the belt on I started the tractor and it would not move, just bogged down. I jacked the back wheels up and found that the rear axle will spin each tire in opposite directions when turned.  I can not get it to unlock.  Any ideas?

Answer
The differential  causes the tiers to turn in one way or the other.  It is normal that one will turn and the other the opposite way at the same time.

Take the belt off.  can you make the transmission work manually? That is put it in gear and turn the input pulley.  Do the wheels turn? Does it lock up?  If not it is the belt routing.  If it does there is most likely something wrong with the transmission.  If it is new it has a warranty even if you install it yourself.