Hello! While I don't specialize specifically in Toyota/BT RRE series reach trucks, I can try to assist you with the information I have. Error code 2:501 typically indicates a parameter issue, as you mentioned. It's good that you've compared the parameters with another truck and they appear to be fine.

Since the error arose after replacing the MCU (Master Control Unit) and loading it with the same software package, it's possible that there could be a problem with the parameter transfer or compatibility with the new MCU. Double-checking the parameters is a good step, but it seems like that hasn't resolved the issue yet.

Regarding the specific value of 255 for parameters, it's true that some systems may use that value to indicate an invalid or default setting. However, I couldn't find any specific information about this value for Toyota/BT RRE series reach trucks.

Given that you have TruckCom, I recommend reaching out to their technical support or contacting a Toyota/BT RRE series reach truck specialist who can provide more specific assistance. They would likely have access to the necessary technical information, troubleshooting steps, and potential solutions for the error code you're experiencing.

If you can provide any additional details about the issue or specific symptoms, I'll do my best to help you further.