I don't know if anyone else has thought of this but it might be that the brake on the transmission has seized. If it has you may have to gently **** the drum with a soft hammer or remove the prop shaft so the vehicle can be moved.
Hope this helps, David.
ffs its a series and your on about 'tapping 'and 'soft hammers'.Or the handbrake is stuck on in which case it tap it with a soft hammer or remove the drive shaft.