Could be the jackshaft is seized or possibly the track is stuck to the hifax. My bet would be the jackshaft bearing since 90% of folks forget to grease it. The grease fitting is behind the secondary clutch (gotta pull the clutch off to get to it).
Jack up the back of your sled so that the track is completely off the ground. Lift the hood and lift the belt cover up. See if you can turn the secondary clutch ( the big one) by hand, which will (should) move the track. There will a decent amout of resistance, but you should be able to turn it. Let us know if you can or can't turn the the clutch and track. One more thing, you should be able to do this without the front clutch moving ( the belt will, but not the front clutch) , let us know about that to.
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