problem with TCP socketswitching on Digi Connect ME 9020

hardware: Digi Connect ME 9020
operating system in example: Windows Server 2008 R2

Sometimes we have problems to change the socket from RealPort to TCP Port. In the moment you try to apply the changes in the weboverview of the router an error appears on the screen:

An error occurs…

Can you say something about that issue? We had this topic for two different customers in the past and would like to know how to fix it.

Thanks in advance

There is a knowledgebase article about troubleshooting Realport
RealPort Troubleshooting for Microsoft Windows

sadly no description found in the knowledgebase of realport troubleshooting.
maybe other suggestions?