If you have recently applied a new hotfix and start running the RTC right away, your RTC client might eventually get disconnected, and a new log on the service tier host machine can appear stating that a new Exception of type “System.ArgumentNullException” has been raised. This can usually happens if you were trying to run a report that was last compiled with the pre hotfix version, and you have not recompiled it after applying the new hotfix bits.
This issue appears because the hotfix runtime has a different signature from what is expected from the previously compiled code and therefore, the .Net runtime will complain that it is not possible to execute the code (which is indeed true).
To resolve this issue, simply recompile the objects in question. It is strongly recommended to re-compile all objects after applying a new hotfix to prevent this from happening (this is especially true if you are applying a hotfix with a build number bigger than 32657).
The general issue will be resolved in an upcoming hotfix, so that the runtime itself will detect if a recompilation is needed, and a message will appear on the RTC stating which object type and number needs the recompilation (and obviously the client will not get disconnected), but until then, please recompile the objects.