Not sure of your specific scenario but, in general, the trick is in remembering that the validation of a control that is *losing* focus only occurs if the control *receiving* the focus has 'CausesValidation' set to true.

OK - that was it. Thanks again. I looked all this crap up in MSDN before posting here, and the topic on Control.Validating Event never mentions this fact. The help might be a little more helpful if it mentioned these things. Maybe we need a Hacker's Guide for .NET < g >