If you find yourself troubleshooting a CPU/COMM error on your VFD make sure to check for a lost keypad or a communication fault. If either of those are the case there might be a faulty connection between the inverter and the keypad. The may also be an inverter CPU malfunction. This applies to IC5, IC5A, IS7 and IPSA models. 

If you find yourself facing any of those problems start by replacing the loader and/or the I/O board then replace either the control or main PCB.