Hi Ravi,
The actual problem is XML namespace is not same for your input payload and the actual message type which you created in the mapping, so you have changed the XML namespace in the message type, but you did not update or refresh message type in the message mapping that is why you still get the same error.
When you delete the message mapping and recreate it uses the latest message type and the mapping works.
So the actual solution for this thread is changing the XML namespace, not deleting the message mapping, can you mark the appropriate reply for this thread then it will be helpful for others who will have the same problem in future.
Deleting the mapping is not good solution, may be you have field to field mapping that is why you did it easily, but if you have more complex mapping then recreate the mapping will take lot of time.
Regards,
Praveen.