SQL Error: State:21000, Native Code: FFFFFCD5

[Bre035]

I have received the error State:21000, Native Code: FFFFFCD5 when attempting to run the following SQL Query to update column using the data from another DB2 Table column.

UPDATE db2prod.arts_case_research
SET
agent_ID =(SELECT db2prod.arts_case_research_AUDIT.agent_ID FROM db2prod.arts_case_research_AUDIT WHERE db2prod.arts_case_research.case_number
=db2prod.arts_case_research_AUDIT.case_number AND db2prod.arts_case_research_audit.audit_action = 'I' AND BUSINESS_UNIT_CODE = 'FM' )
WHERE db2prod.arts_case_research.case_number = (SELECT db2prod.arts_case_research_audit.case_number
                             FROM   db2prod.arts_case_research_audit
                             WHERE db2prod.arts_case_research.case_number
                             =db2prod.arts_case_research_AUDIT.case_number
                            AND  db2prod.arts_case_research_audit.audit_action = 'I'
                            AND BUSINESS_UNIT_CODE = 'FM');