If your VFD is throwing a H/W Diag fault error there are three main sections to check. You will want to look at the EEP ROM, ADC Offset and the Watchdog. The EEP ROM is associated with memory fault, the ADC is associated with current feedback circuit fault while the Watchdog looks for CPU malfunction. 

In the case of EEP ROM an error may occur at initial power input after O/S downloading. Regardless, if any of the three sections are not properly set-up then replace the control and/or main PCB and make sure to replace the DM-CT or CT wire as well.