Intermittent "UDT not defined" error when compiling VBA but code runs without errors

I'm building an Access database and I'm getting a "User-defined type not defined" error when I compile the project using Debug > Compile, but the database opens and runs without any runtime errors, and everything seems to work. No location in the code is given, just an error dialog.

The UDT error doesn't happen every time, but it does happen most of the 开发者_StackOverflowtime. If I don't have any forms open when I compile and I have recently opened Access it seems to work. If I open a form and try again (after making a superficial change so it will allow me to recompile) I get the error.

This is not true consistently however. I often get the error when no forms are open, but I ALWAYS get the error when forms are open. It doesn't seem to matter if they are open in design or form view.

What could be causing this? What kind of error should I be looking for?

Using Access 2010.

Thanks HansUp, a decompile seems to have resolved the issue. The instructions you linked were helpful.