>Well - I found the problem. After removing every method, property, object (almost) to narrow down the problem, I went back to check the properties of the remaining 3 objects.
>
>I had checked the properties of all the form objects, but did not check the form properties. It turns out that the 'Tabstop' property on the FORM was .F.. This must have been accidentally set somehow as I have never used, nor even known that there was a TABSTOP property on the Form itself. Turns off this disables / enables tabbing on the entire form.
>
>So, hours later, I have learned something new today. Thanks very much for your suggestions.

Glad you found it - haven't occurred to me to check on the form's level.