The following causes are probable for persistent Err. display:
1. The terminals RES and SD are always short-circuited.
2. Operation panel contact or operation panel itself is faulty.
3. Inverter is faulty.

If the inverter can be operated from the external source while "Err." is displayed on the operation panel, the cause (2) is highly probable. Check connection between the inverter and operation panel again.
If the inverter cannot operate, the cause (1) or (3) is highly probable.