It's not really unheard of for error messages in Access 'not fitting the situation!'
Also, although we usually think of Forms, and even entire Databases, when we speak of corruption, Controls, such as Command Buttons and Comboboxes, can and do become corrupted, and seem particularly susceptible to this during app development. The test/cure for this is short and simple...delete and then re-create the Control.
If a new button repeats the error, you'd have to think about the Command Button Wizard, itself, being corrupted.
Linq ;0)>
The problem with making anything foolproof...is that fools are so darn ingenious!
All posts/responses based on Access 2003/2007