Jared,
Turn your EO Config up so that you can see the hex dump of the message as it is going out. Then check to see if the segment terminator is at the end of the MSH (it appears that is the complaint the receiving system has).
If it is there (I suspect it is), share the information with the receiving system vendor and indicate you think they have a problem that needs correction.
Jim Kosloskey
email: jim.kosloskey@jim-kosloskey.com 30+ years Cloverleaf, 61 years IT – old fart.