Access 2003 combo box acts like it is locked, but it is not

I am designing an Acces开发者_如何学Cs 2003 form (continuous) with a combo box in the form header. This combo box has as a row source another table that is unrelated to the form's record source.

I have created the combo box and set its row source to the table i want. When I click on the combo box arrow, I see the values I want in the drop-down. I can even mouse-over them and see them turn bold. But I can't actually select any of the values. In other words, it is acting like it is locked when it isn't. How do I select a value in the combo box?

(If you're wondering, once the user selects the value, an event will open up a 2nd form based on that value)

Items to check:

1. are the combo box properties Enabled = Yes and Locked = No?
2. does the form allow edits?
3. is the combo bound to anything (Control Source property)? If so, what?
4. try message box or Debug.Print statements from your combo's After Update, On Enter, and On Exit events to see if you can figure out what's going on