Open any code module (or open the Immediate Window, using Ctrl-G, provided
you haven't selected the "keep debug window on top" option). Select Tools |
References from the menu bar. Examine all of the selected references.

If any of the selected references have "MISSING:" in front of them, unselect
them, and back out of the dialog. If you really need the reference(s) you
just unselected (you can tell by doing a Compile All Modules), go back in
and reselect them.

If none have "MISSING:", select an additional reference at random, back out
of the dialog, then go back in and unselect the reference you just added. If
that doesn't solve the problem, try to unselect as many of the selected
references as you can (Access may not let you unselect them all), back out
of the dialog, then go back in and reselect the references you just
unselected. (NOTE: write down what the references are before you delete
them, because they'll be in a different order when you go back in).

Just so you know: the problem will occur even if the library that contains
the specific function that's failing doesn't have a problem.