I'm not making any sense of the criteria string - perhaps because what it applies to is missing. If this were a date comparison like
WHERE [tblOrders].[TheDate]Between [myTextbox] And [MyTextBox2], the first part makes sense. The second part does not
Or [myTextbox] Is Null And [myTextBox2] Is Null
If a textbox has no value in it, the function will return True when it evaluates. So the latter part of what looks like a where clause becomes
Or True And True which makes no sense to me.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.