Not sure why you are not getting an error message when using other
language drivers.
The C# driver error message indicates that the server at
61.55.187.14:40000 is not a member of a replica set. Can you execute
the following mongo shell command to verify whether that server is a
member of a replica set or not?
C:\mongodb\mongodb-win32-x86_64-2.0.0\bin>mongo --host localhost --
port 27017
MongoDB shell version: 2.0.0
connecting to: localhost:27017/test
> db.isMaster()
{ "ismaster" : true, "maxBsonObjectSize" : 16777216, "ok" : 1 }
>
In the above commands replace "localhost" with "61.55.187.14" and
"27017" with "40000".
The output above is for a server that is NOT a member of a replica
set. Please post your output for comparison.