It is due to a conflict of server & client version.
Can you please download and install the latest Output Messenger Server & Client version from online
http://www.outputmessenger.com/index.php/downloads/
To update Server:
1. Stop Output Messenger Server Service, if running.
2. Exit Output Messenger Server Manager tool if running.
3. Install new updated server over existing version
4. Start the Service.
To Update Client:
(Need to update the same new version in all the clients)
1. Exit Output Messenger if running.
2. Run the installer in client or push MSI installer using Windows Group Policy.
