Linked Server Query Error

SQL 2000
I have a process that calls several stored procs which access a database on a linked server.
code that fails:

SELECT DISTINCT em.er_id, em.er_name, bp.bpo_id, bp.bpo_name
FROM [dbrptc13dayoldprod].ues.dbo.Employer em
Inner Join [dbrptc13dayoldprod].ues.dbo.BPO bp ON
em.er_bpoid = bp.bpo_id

Error message:
Server: Msg 913, Level 16, State 8, Line 1 Could not find database ID 6. Database may not be activated yet or may be in transition.

The database is accessible from query analyzer with a simple select from the linked server. Also if I change any letter in the ues.dbo.Employer em or ues.dbo.BPO bp part to a different case it works fine.
For example: -changed the BPO to BPo- this works!
SELECT DISTINCT em.er_id, em.er_name, bp.bpo_id, bp.bpo_name
FROM [dbrptc13dayoldprod].ues.dbo.Employer em
Inner Join [dbrptc13dayoldprod].ues.dbo.BPo bp ON
em.er_bpoid = bp.bpo_id


Please help I can't figure this one out.

Thanks.