Paul,

Just a guess from my co-worker, Bill Mason, but if you are doing this in a form, forms in VMP have private data sessions, and so if you are trying to open it exclusively in the form, it may already be open in the default data session, and so preventing you from getting exclusive access.

You can see this using the set command. The tables are open once in the default, and again in the form's data session.

HTH
Bill (and Bill)