Hi ehsank,
if you've checked all the compatibility notes listed in the Change Log between your old version and the 5.1.1, and in the case applied the appropriate actions, then your old code (both client and server side) should work.
In order to investigate further the issue could you check in the server log ("Lightstreamer.log" file under the "logs" directory) looking for messages like this:
Finished loading Data Adapter <Andapter Set Name>.<Adapter Name>
for all the Adapters you have deployed? Please check if the "LightstreamerLogger.init" is set to INFO level at least.
If all the Adapters start correctly, please can you check if when your client try to connect to Lightstreamer server some error or warning messages appear in the log?
