Seems you got it: not all of the fields in the view have proper values, or empty fields are treated as NULL. So you need to populate fields as needed; append blank does not do it.

>I have done some testing and it seems if I do the following it works.
>
>select tester_v
>append blank
>replace tester.pkfield with 'AA', tester.code with ' '
>
>then tableupdate works.
>
>If I do the following:
>
>select tester_v
>append blank
>replace tester.pkfield with 'AA'
>
>then tableupdate() fails with Oracle giving a cannot insert nulls message.
>
>Jason