Help with If Then statement

Hi all,

I have an if then statement coded as an after update event procedure on
a data entry form. It works perfectly on an Access 2000 database, but
when I try the same query on an Access 2002 database I get a "variable
not found" message. I have verified that the field names are correct
but I still cannot get it to work.

The query is as follows:.

If [MaritalStatus] = "Married-Living Together" Then
[SpouseName] = IsNotNull
[SpouseName] = Null
End If

Is there something I am missing, or something that changed between the
two versions of Access?

Any help is greatly appreciated.