[COLOR="Purple"][I]The problem in your case is almost certainly that the
control is bound to a column of Boolean (Yes/No) data type. a Boolean column can
only be TRUE or FALSE, which in Access are implemented as -1 or 0, so can never
be Null. So in any row in a table a Boolean column can only be TRUE or FALSE,
never NULL. By default it is FALSE. You can, however, paradoxically set the
DefaultValue property of a Boolean column to Null, and similarly of a control bound
to such a column, as you have done. This is pointless, however, as the value will
become FALSE as soon as you begin to enter any data in the row, which is what is
happening in your case.
You'll be pleased to know that there is a simple solution to this: Change the data
type of the column in table design view to Number and its Length property to
Integer. Make sure its Required property is False (No) so that it allows Nulls, and
set its ValidationRule property to:
True Or False Or Is Null
You now have 3-way logic, TRUE, FALSE or MAYBE, which incidentally was one of
Codd's original requirements when he introduced the database relational model
back in 1971.[/I][/COLOR]
