when the user opened it on their system the report window failed to open
Sounds like maybe an issue with Trusted Locations or the fact that you're "sending" the db - assuming this means by email. When this user opens the db, are there any warning dialogs? Does it have a message bar at the top of the Access window that indicates protection has been automatically turned on and code/macros have been disabled? Or is all this moot because code/macros run for everything else?
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.