Hi,
Thank you for posting in Symantec community.
I would be glad to answer your query.
According to Microsof documentation, the most common cause would be as follows:
"This issue may occur if the user profile was manually deleted by using the command prompt or Windows Explorer by a user or by some program. A profile that is manually deleted does not remove the security identifier (SID) from the user profile list in the registry. Since the SID is still present, Vista (or Windows 7) will still try to load the profile by using the ProfileImagePath that points to a nonexistent path. Therefore, the profile cannot be loaded".
This list can be found in the Regsitry at:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
Reference
"The User Profile Service failed the logon. User profile cannot be loaded"
http://www.symantec.com/docs/TECH131866