Did you remove the valve block at any stage? I would say the manual piston has been installed backwards, this is the piston that should be locked into the quadrant.
Does it drive forward in all gears when in manual mode?
Assuming someone hasn't been trying out their Christmas prezzie spanner set. If you have first and third gear, rule out a clutch problem and suspect a broken brake band or the number 5 control solenoid. Or it's electrical connectors of course.