Hi Soumyaghosh,
The specific error code and message seen in the screenshots is warning of outgoing spam. Chances are, that computer has been compromized and is being used by a remote party to send spam out into the world.
The articles and threads that were recommended above provide excellent advice: please do remove that computer from the network before it can send any more spam, perform a full system scan with teh latest defintiions, and if need be conatct Symantec Technical Support for help in identifying any suspicious files that are making this computer part of the spammer's botnet..
Thanks and best regards,
Mick