Hi Varadarajan,
The GA version of AsyncOS for WSA is 7.5.2-118. You are running 7.1.1 so I would recommend you to upgrade to GA version.
You can find GA info at:
http://www.cisco.com/web/services/acquisitions/ironport.html
Is your WSA directing accessing the Internet? I am asking because you could be having the traffic from WSA to another proxy/filter. In order to get updates, I would also recommend you to review the traffic from the WSA to the Internet, to make sure the device can reach the update servers.
A packet capture may help.
For this type of issue, I would recommend opening a TAC case.
I hope this helps.
Regards,
Valter