Hello,
If I recall correctly Windows XP las day of support was on August 2014.
According to Cisco documentation the supported versions for OS on AnyConnect 3.1 are from Windows 7 and above. Below the document for reference.
http://www.cisco.com/c/en/us/td/docs/security/asa/compatibility/asa-vpn-compatibility.html#pgfId-213802
Also the same document had a link informing the EOL/EOS for the AnyConnect 3.x version.
http://www.cisco.com/c/en/us/products/collateral/security/anyconnect-secure-mobility-client/eos-eol-notice-c51-734084.html
Regards,
Miguel