I'm not sure I understand?

Which field is returning the Cannot be Null? Is that field definition allowed to except NULLS? What kind of field is it, Primary, Unique?

Primary's wont allow nulls full stop, uniques will allow a single record to have a null value, as duplicates are not allowed.

Does this help?

If not post up some more information about the table and trigger.

Jon

>I am trying to create an instead of trigger that builds a unique key based on other items inserted into the table. My trigger works fine if I put any bogus/temp value into the unique key field, but gives a: 'Column can not be null.' error if I try to enter the data without anything in the field.
>
>Is there a way around this, or do I always need to insert a temp value to satisfy the key field entry?