Hello-
Usually LabVIEW's "explain error" can identify all errors. Not so in this case. It must be an instrument driver specific error. It may help to use highlight execution to trace through the VI to find the source of the error.
There was a driver for the 4000 on ni.com/idnet, but it was contributed. If further assistance is necessary, it may help to contact the developer of the driver. It is likely the instrument manufacturer, Newport.
Randy Solomonson
Application Engineer
National Instruments