Error 2474

[mscertified]

"expression entered requires the control to be in the active window"

Any idea what causes this and how to fix it?
The statement is 'subformname = screen.activecontrol.tag'
In debug, referencing screen.activecontrol causes the error

This is being run from the current event of a form.
The focus has been set to a control.

 

[Baz]

In debug it would, because the debug window is the active window!