This error message (visible in the Log Messages section) occurs when a location that is set up for ISO requesting in RACER, uses a Generic Script (GS) method to request - either via Amicus or the RACER online request form. There is no way to fix a request with this error, nor is there a way to action the request such that the borrowing library will see a message. You will not be able to indicate Shipped, Received, Message, Conditional, etc., instead the request stays at In Process / Check Error.
The two options for this type of "Check Error" request are:
1. Contact the requesting library by phone or email and ask them to resubmit the request using their ILL system.
2. Track the progress of the request outside of RACER using email to communicate with the requesting library as needed.