Im using the leave event of a text box

Try this
under click event of cancel button do like this
canclebutton.CausesValidation=false

due to this cancel button executes before doing any validations
you can also set this property by right clicking on button and set cause validation to false

This is very interesting.

In C++ there is something called MFC. MFC has a very sophisticated ability to perform validation. Experienced MFC developers would insist that it is very poor design to validate fields when an Okay button is clicked.

I am neutral. It does not matter to me; both ways can be useful, depending on requirements. It is interesting that people can be so adamant (demanding) that one of the two options are the only good way.

Except I will say this much. Microsoft C# programmers seem less object-oriented. They don't use derivation as much as Microsoft MFC programmers do. An object-oriented solution to validation would be done by deriving a control from a control and do the validation in the derived control. That would be entirely possible if the validation did not include other controls. Validation logic such as what MFC has would include logic to avoid validation when the form is canceled. I am surprised that .Net does not.

That's fair enough if it's a 'change password' dialog.

I thought when I read the question that it was just a normal 'logon' dialog though I see from the addition to your original post that you've figured out a way to avoid validation in the Leave event in any case, if the user presses the cancel button.

the username and password are being entered on a change password form - i thought if it is validate as they finish typing they wont get annoyed by entering username, password, new password and cofirm password - only to be told the username (first entry) was invalid - so annoying.

But i have done what u said on the normal logon form.