Transmission Error Code RPM Sensor 3

[Retlas]

Hey, just wondering if anyone knows what the issue is with my transmission. For the last year I have been experiencing a little jolt now and then in the gear shifts and not being able to change to sports mode whilst this would happen and the car would Rev higher than normal, normally this would go away once I turned the engine off and back on again. But yesterday it got really jolty and abrupt and now even if I am in park when I pull my gear stick down to reverse it’s a real big jolt backwards and a big jolt forward when it is in drive and I can only drive in 1st gear it won’t shift! Had RAC out today to plug into a computer and there was a error code RPM Sensor 3 ??? Does anyone have any idea what this could be? Thanks.