You're referring to the ActiveControl, but this error (the setting you entered isn't valid for this property) pops when you're attempting to set a property of a Control or other object, in code...not during data entry, which kind of sounds like your objective, here.
Are you, perhaps, wanting to change the error message if inappropriate data is entered in a Control...i.e. entering Text in a Number Field?
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The problem with making anything foolproof...is that fools are so darn ingenious!
All posts/responses based on Access 2003/2007