Error 'ORA-01722 invalid number' being returned with WHERE clause

Hi all,

I can't quite work out what's wrong with the following query. When it's executed, I get an error saying 'ORA-01722 invalid number'. I've narrowed down the issue to the WHERE clause 'AND fad.document_id = fdt.document_id(+)' and when this clause is commented out, the query fetches all records successfully.

 I'm thinking there is a data issue as I don't have this problem in other environments, but how can I locate the troublesome record?

Any help will me appreciated.

Michael

SELECT vs.vendor_site_id, vs.vendor_site_code, vs.vendor_id,

          ve.vendor_name, vs.org_id, op.NAME, vs.vendor_site_code_alt,