ignition signal primary,
check that the ignition coil harness earth is connected. check cas. an r34 4 door that had this problem needed a new ign coil, put in splitfires and all was fine. try swapping out with someone nearby if they are generous
d/c the battery overnight or longer, hopefully will reset the tranny ecu. if the problem comes back straight away, there is definitely something wrong in there. if it comes back after a few min or after a drive etc... maybe try mentioning what you had done with it eg overdrive button etc. gearbox problems could be quite bad for you
talk to just jap if you bought it recently enough