Mower won't move

[CyndiB]

Hello, I'm new to this forum, and have a Craftsman 42" lawn tractor with the 15.5 HP Kohler engine, automatic transmission, model 917.271064. Today before starting it, I disengaged the freewheel lever so I could pull it backwards a bit in order to put gas in it. Then I re-engaged the lever, started it up and backed it out of the garage. When I put it in 'forward' it would not move. Now it won't move either backward or forward. All the belts are snug and in place. The gear lever moves normally. When I disengage the freewheel lever, it will roll just as it's supposed to, and when I re-engage the lever, it won't move, just as it's supposed to. I have not taken off any wheels, and I tried the transmission purge with no success. I last used it 2 weeks ago with no problems. Can anyone tell me what might be wrong? Thanks