Just got round to having a look at the machine, got the original machine parameters from the guys at denfordata.com and checked them. No problem there. Wiring all looks good, double checked all the connectors were okay.
Today I unplugged the motor and encoder from the x axis servo drive, still got the error plus one more for unplugging the encoder.
Then I tried swapping all the cables to the x and z servo drives, now the 441 error is on the z axis. So I guess that points to a fault with the servo drive. Unless anyone can think of anything else it could be?
Does anyone know of a good company that could repair or replace the drive?