First step is to double check that the shifter isn't the culprit, make sure that the two bolts are nice and tight and that the housing hasn't moved at all, Second step is to pull the inspection cover at the rear of the tunnel and look at the shift rod coupler, make sure that it's tight and as it should be.
THEN you can start to worry about the trans being caught in gear. If it turns out that it IS, sometimes disconnecting the coupler, sliding the shift rod towards the front and gently hitting the transaxle shaft with a lead hammer will get it to move freely, I've had some luck by doing this.
Otherwise, check the tail housing bolts, if they're lose, you're lucky, tighten 'em up and see if everything is good to go. If not you'll have to loosen them to remove the tail housing and check to see that the "hockey stick" is engaged with the transaxle. It might have become disconnected or slipped past the end of the rod or broken altogether and need replacement.
Otherwise, it's an internal problem that's kinda serious, and you'll need to contact the builder for some relief.
Luck,
TC