When you drop down a combobox, there are 3 things that can happen and here are the ways to trap them:

1. InteractiveChange will fire if you choose an item
2. Click will fire if you click on the Text part of the combo, or back on the Drop Down button to collapse it.
3. The way to trap a click on another object (the form, a textbox), is the Valid event that apparently fails if the List is dropped down.