ERROR: could not open relation 16388/24734/51896: Cannot open or remove a file containing a running program.

Hi
While running a VACUUM ANALYZE
The process aborts and I receive the following message in the log:

ERROR: could not open relation 16388/24734/51896: Cannot open or remove a
file containing a running program.
STATEMENT: VACUUM ANALYZE

51896 refers to an index on a table with over 10,000,000 rows.

The process runs nightly with this being the first time I have a problem.
It runs at 2:45 am where there should be no contention.

select version() ;
"PostgreSQL 8.2.6 on powerpc-ibm-aix5.2.0.0, compiled by GCC gcc (GCC)
4.0.0"

Any input would be appreciated.

Keith Kreuzer
ext 3424