You really should be using, as combo mentions, the Click event of the control.
Say you have a frame with two option buttons in it. Clicking an option button - to select it as True - will indeed fire Frame_Enter...but it will fire before you get at the control.
Example:
optButton1 is not selected (= False)
optButton2 is not selected (= False)
Clicking either button, your code returns nothing as neither control = True.
optButton1 is already selected (= True)
optButton2 is not selected (= False)
Clicking optButton2 - assuming focus is indeed outside the frame - will indeed display "optButton1". However, after the message is displayed, you will have to click optButton2 a second time. What is the point of that?
Further, say optButton1 is true (optbutton2 is false) and you click optbutton2, if you are clicking between them, then Frame_Enter is NOT fired, so even though which button is True changes, you do not get a display.
Better to use the Click event of the control, although I fail to see the actual point of this at all, really.
What is it you are trying to achieve?
Gerry