PostgresQL 55000 error

I've recently had a database I'm developing grind to a halt with error
55000, apparently connected to a "select nextval('softdbk');" statement
I'm using to generate soft DBKs. These are integers - none have yet
exceeded 5 figures (63195 on the production database, 10 on the test
database). Neither database can currently be updated.

I'm running Postgres 8.2.7 under Fedora 8, kernel 2.6.25.4-10.fc8. The
application is using current JBDK drivers and was compiled and run under
JDK 6.0_05. The application was running OK until 2-3 days
ago, when it suddenly started throwing 55000 errors.

The sequence select statement is being caught and reported by my exception
trap, so its the obvious immediate culprit. I'd made minor changes to the
application around this time, but nothing that should have affected
database access at all: the class containing all database access
methods for the affected program was not changed at all.

I'm using a single sequence to generate soft DBKs for use as the prime
keys of all tables. Before you ask, the natural keys are all long (80
characters or more), so soft DBKs save a lot of space and probably make
joins faster.

If you've seen Postgres 55000 errors I'd like to know the circumstances
and how you resolved them as it might give me a clue about is causing
this. There is nothing obvious in the logs. Recreating a test version of
the database hasn't helped. The sequence select works OK from psql.


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