Hi Mike,
X12 EDI in BizTalk 2004 was painful to say the least. BizTalk 2004 shipped with the ‘Base EDI Adapter’ which is a stripped-down version of the commercial Covast EDI Accelerator – it contains only a small number of message schemas that were shipped with the full product.
If you can, I would suggest upgrading to BizTalk Server 2006 R2 or (preferably) BizTalk Server 2009, which comes with in-built EDI functionality (i.e. no thrid-party add-ons) and supports the full EDI X12 message set. If you are stuck with BizTalk Server 2004, can you specify which message/s you are trying to work with and I can advise whether they are available in the ‘Base’ adapter.
Rgds, Nick.