Hi Shivendra,
Well by seeing the excerpt from the log you've posted, your private key passphrase seems correct and the mail should be in general decrypted. Since it is not behaving as expected we need to investigate it in detail.
Can you please test by sending an encrypting email to yourself and attach a complete log file? Suppose your email address is test@test.com and this email address is also attach to your keypair. For the test purpose, you send an encrypted email to your email address and check whether the email is automatically getting decrypted or not. Once you have done that, please attach the log file into this thread.
You may want to check this knowledge base article which clearly describes how email is encrypted and decrypted using Symantec Encryption Desktop (previously known as PGP Desktop) software. You may find some useful information / concepts there.
http://www.symantec.com/docs/TECH176320
Best Regards,
bipshr