Hi Mangesh,
I've been looking at the logs and code and the only reasonable explanation I have is that your auto serializer config on the client (on which the error is getting thrown) is not correct and that the particular class is not defined in the patterns.
Could you explain your complete topology please - how many servers are running? How many app servers (GemFire clients)? Do you have a load balancer? Are you using sticky sessions?
--Jens