There were no entries in the Journal messages under eConnect_Incoming Private message queue in Computer Management or in the eConnect section of the Windows Event Viewer. Once the message had left the client machine no trace could be found.
We connected to the client site and ran a test script on the GP/eConnect server, on a different server and on different clients; all worked without problem.
The client then took over testing and ran it on different clients logged in as different users and found that it worked on some and not on others. I suggested trying the original client machine again, the one which the missing eConnect messages was first reported, and it was found that logged in as the original user the messages still went missing but logged in as a different user they poisted successfully to Microsoft Dynamics GP.
The client decided to add the user to the Local Administrators group on the GP server and received an error mesage stating that the server had lost trust in the domain. After stopping SQL Server and the eConnect service, and setting both to Manual start, the server was removed from the domain and then added back on.
Once SQL Server and eConnect were restarted, and set to Automatic start, the test was run again; successfully from all clients and all users. Based on the pattern of success and failure of the posting, it seems the error was restricted to those users who had changed their passwords after the GP server had lost trust in the domain.