Is the belt slipping off of the transmission drive pulley. If so then check the tranny support bracket to make sure it is still attached to the tranny. Some of the Husqvarna mowers has a bracket on the center front that would break the bolts off, strip the bolts out of the tranny, or in some cases break the bracket. If the bracket has come loose also look at the frame where the axles connect to the frame for cracks.