try this for attaching files
https://www.accessforums.net/showthread.php?t=70301
If your field is on a subform, likely the subform reference isn't correct. You can usually determine this by opening the subform directly (as long as it doesn't rely on some other object that isn't open). If the subform opens without prompting, the issue is usually a reference to the subform that's made from the main form, regardless if that reference is something on the form or in the query that's behind it.
referencing CONTROLS on subform:
[Forms]![Main form name]![subform control name].[Form]![control name on subform]
NOTE: subformControlName may not be the same name as the subform itself
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.