I've had this one too...
For me the reason was that the form was trying to carry out an action on table data on the ONOPEN property, but because there was no data in the table, I got this message.
If there is no data in your table underlying the form, put a dummy record in to start it off. You can always delete it after the table has gained some weight.
It is a 'get around' and some might say it was bad programming.
But what the hell....it sorted it.
Dave E