We had an overseas client call for help with a failing eConnect integration, it was failing with essentially no error at all.
The last time this happened, it was because of an error in an Multi Currency trigger in the Dynamics database, today's error turned out to be a missing currency line in DYNAMICS..MC00200. The trick was finding the error, because it wasn't being reported.
We had the XML, and it had three call: PO Line, PO Header, and PO tax. We already have 'wrapper' code on this site for the first two so I wrote the wrapper below for the tax call and sent it to them.
We copied the XML into the three stored procedure wrapper calls and we got the error on the header: error on the MCValidate stored procedure. And... an error number. I looked up the number and it was 'missing MC00200 line'. Grrr.
Hope this helps.