Hi,
I have seen this error before when an invalid IAK file reference was wired to the FP Open VI. If you have an IAK file wired to this VI, then I would remove the wire. The FP Open VI will open the last saved IAK file by default if it is not wired.
This also may be occurring when the FP Create Tag VI has an invalid "comm resource name", "device name", or "item name".
Hope that this fixes the problem,
Regards,
Mike