> Oops, I forgot index problems could lead to there being NULL or
> duplicates in the PK field, so change the above query to:

> select
> T.F1+0,
> T.F2+0,
> count(*)
> from
> T
> group by
> 1, 2
> having
> count(*) > 1

SET and Thomas, thanks for the answer.
The above select statement was only to make sure that no duplicates
are still in the table.

The table is a completely new creation, and nobody else could have
been using it besides me, although the database itself is the original
production database used by some 50 concurrent users.

I disconnected and reconnected, even did a backup (to "visit" each
record) and explicit sweep and made sure noone else was connected
to the database late in the evening. No success.

Today anyway, the problem dissolved into nothingness. I could suddenly
create the UnC quite fine. Go figure...

Thank you anyway, guys.