Unable to connect to Bitcoin core testnet remote

[simplynabh]

Hello everyone,
I'm unable to connect to Bitcoin core testnet installed on windows server machine (remote). I'm using Nbitcoin.dll to connect to the same programmatically (C#).  At times it says - "unable to connect to remote server". I change the port to 18334. Now it says - its Unexpected character encountered while parsing value: <. Path '', line 0, position 0.

Please suggest how to proceed.

Thanks in Advance.