>How many of us have inadvertently caused this error? Perhaps it was done by calling another form (e.g. lookup form) from the Valid event of a textbox and somewhere along the way, a specific control needs focus so we call Control.SetFocus().

I suppose you just have to realize that When() and Valid() are for determing if an object can get or lose focus... not where it shoudl go next or popping up a form to correct the data its trying to validate. It makes sense if you think about who's responsibility it is to do things other than "can I enter/leave".

Though returning a numeric from Valid() defeats that thinking, you know what I mean.