EFS encrypted files on the Desktop or in the Documents folder cannot be decrypted on Windows Vista when Symantec AntiVirus 10.2 client is installed
On a Windows Vista based computer that runs Symantec AntiVirus 10.2 client, you enable EFS for documents on the Desktop or in the Documents folder. After you reboot the computer and log on again, the encrypted files cannot be decrypted.
The problem does not occur when folders are encrypted in other locations.
Also, when Symantec AntiVirus is uninstalled the problem goes away.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB953799.