Exchange 2003 and ID 1705

My Exchange server is occasionally throwing up a 1705 error:

An unexpected error is forcing EXPS to close the SMTP connection to "SERVERNAME". "CSessionContext::OnEXPSInNegotiate" called "HrCheckClientPermissions" which failed with error code 0x8009030c ( f:\tisp2\transmt\src\smtpsink\exps\expslib\context.cpp@1819 ).

The server that is lists in SERVERNAME is another internal server... but that other server isn't an Exchange server so I'm not sure what might be causing this (as most references when I googled talked about problems communicating with another exchange server).

Any thoughts?

The X-EXPS verb is an Exchange proprietary extension to SMTP. It should only be used between Exchange servers within an organization. Have your "other server" authenticate using the AUTH command instead.