How to validate sum of fields (access 2003)

Hi,

I'm running a query in order to find records that have at least one match,
based on a form - where I select a certain record - and a subform - where the
matching records are displayed. The search is based on four parameters
(located in the main form), which are scored from 0 to 1 (passing through
0,25, 0,5 and 0,75). The results that appear in the subform are ranked and
filtered according to the sum of those four criteria and corresponding scores.

Now, my problem is very simple but so far I haven't found a solution that
works: I want to validate the sum of those four criteria scores so that it
doesn't exceed the maximum possible score (=1); in case this condition isn't
met, the query shouldn't be updated.

I've tried putting this piece of code in the (main/sub) form's properties
(namely, in the before/after update event) but it isn't working:

If Score1 + Score2 + Score3 + Score4 1 Then
MsgBox "Verify sum"
Cancel = True
Me.Undo
End If

Thanks in advance,

Paula