adding details on SessionLockLostException

Author: Ashish Chhabria

articles/service-bus-messaging/service-bus-messaging-exceptions.md

@@ -114,7 +114,7 @@ The lock on a message may expire due to various reasons -
 
 ### Resolution
 
-In the event of a **MessageLockLostException**, the client application can no longer process the message. The client application may optionally consider logging the exception for analysis, but *must* dispose off the message.
+In the event of a **MessageLockLostException**, the client application can no longer process the message. The client application may optionally consider logging the exception for analysis, but the client *must* dispose off the message.
 
 Since the lock on the message has expired, it would go back on the Queue (or Subscription) and can be processed by the next client application which calls receive.
 
@@ -124,8 +124,19 @@ If the **MaxDeliveryCount** has exceeded then the message may be moved to the **
 
 ### Cause
 
+The **SessionLockLostException** is thrown when a session is accepted and the lock held by the client expires on the service side.
+
+The lock on a session may expire due to various reasons - 
+
+  * The lock timer has expired before it was renewed by the client application.
+  * The client application acquired the lock, saved it to a persistent store and then restarted. Once it restarted, the client application looked at the inflight sessions and tried to process the messages in those sessions.
+
 ### Resolution
 
+In the event of a **SessionLockLostException**, the client application can no longer process the messages on the session. The client application may consider logging the exception for analysis, but the client *must* dispose off the message.
+
+Since the lock on the session has expired, it would go back on the Queue (or Subscription) and can be locked by the next client application which accepts the session. Since the session lock is held by a single client application at any given time, the in-order processing is guaranteed.
+
 ## SocketException
 
 ### Cause