André wrote
<<
...
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.
...

>>

A couple of times I've seen problems vanish just
by stopping/starting the Firebird service. Maybe
just closing all connection or, at worst,
restarting the service. Those problems occured
after some metadata change (with connected
users). The latest one was desctibed in a
message to this list on January 14. (Subject:
Firebird error: partner index description not found).
Maybe you did some tinkering with the metadata?

--
Aage J.