Not sure how to solve your current problem of not seeing the global variable. But I have a creative workaround for you to explore.
You could use the USERDATA metadata field for the message itself. Using msgmetaset within your FTP Dir Parse, you can set the filename for the message, which will carry through to the IB Data TPS where you can retrieve it useing msgmetaget.
Hope this works
Bob 8)
Robert Milfajt
Northwestern Medicine
Chicago, IL