Hi Peter,
you can't customize the built in message box.
However you can create a dialog form to use in place of a message box.
When you need to open your own message box, pass it the error message you
want to show and customize its appearance as much as you like.
I have just created a custom form to use as a message box for one of my
apps.
I pass not only the message but also the captions for the buttons.
Jeanette Cunningham MS Access MVP -- Melbourne Victoria Australia