I don't know if this is the cause of your problem but it may give you somewhere to look.
According to M$:
CAUSE
Your database contains a reference to a database, type library, or object library that is marked as "Missing:" in the References dialog box.
RESOLUTION
Follow these steps to remove the missing reference:
Open your database.
Open a module in Design view.
On the Tools menu, click References.
Click to clear the check box for the type library or object library markedas "Missing:."
An alternative to removing the reference is to restore the referenced file to the path specified in the References dialog box. If the referenced file is in a new location, clear the "Missing:" reference and create a new reference to the file in its new folder.