Cannot contain Null Value

[Dorothy]

I have a data entry form that consists of 4 tabs. The
first 2 tabs and the 4th tab places the information that
is entered into the same table. The information that is
entered into the 3rd tab goes into a different table,(and
is a subform)that is linked by an ID from the 1st table.
I have these tabs in a specific order since our
application form flows in this order. I have specified
that certain fields cannot be left null in the 4th tab.
So when enter data we fill in the first 2 tabs then start
to enter the 3rd (which is going into another table) I get
an error message that says FieldName (under tab 4) cannot
contain a null value because the Required property is set
to True. We aren't leaving it null, just haven't got to
tab 4 yet. Is there a way around this? This sounds
confusing even to me, so if you have questions please
ask. Thanks.

 

[Bob]

Access is trying to save a record that is comprised of
fields from tab 1, 2 and 4 as soon as you move the focus
to tab 3 - the subform for a different table. Since the
record doesn't contain a value for a field that you've
identified as "necessary" on tab 4, the error message
appears. Maybe you need to look into putting the fields
from tab 4 into a separate, related table.