The Symantec Endpoint Protection (SEP) client installation fails at the very beginning of the installation process, with an error that indicates the Windows Installer Service can't be accessed.
The Windows Installer is corrupt.
These steps are provided for your convenience. For further assistance in troubleshooting possible operating system corruption, please contact Microsoft support.
To check the permissions on the registry key, perform the following steps.
NOTE: Be sure to back up the registry before proceeding:
"The Windows Installer Service Could Not Be Accessed" error message when you install a program in Windows XP
"The Windows Installer service could not be accessed" error message when you try to install Office