ArchiCAD can give this error,
-if the MEP library is not loaded, or not the complete library is loaded
-if the MEP tools have wrong defaults, so all MEP related tools in ToolBox should have a valid MEP object as default (routing uses the defaults to create the system)
So I think this error is not related to TeamWork, check your tools and the library.
Yes, the problem was related to the second thing. The Template for some reason didn't assign any objects to MEP tools. Now that they were assigned, routing works fine. Indeed its not a TW problem, maybe a moderator could move the thread and rename it.
I'm happy the problem was solved, thanks Marton!
Anyway the warning message is completely misleading, and should be changed to something more relevant.