Harry,

I think of Valid and LostFocus as follows;

Valid is used to determine if focus will be allowed to leave a control
LostFocus is used to respond to focus leaving a control

The same with When and GotFocus;

When is for determining if focus will be allowed to arrive at a control
GotFocus is used to respond to focus arriving at a control

In your case, bringing up the other form is really having the current control lose focus, as focus goes to the other form, so it is best hadnled in the LostFocus event.