Can’t complete MS Security Essentials installation on WinXP

As I was trying to install the Microsoft security essentials, I encountered this error message “0×80070643″ Installation encountered a problem.
Can’t complete the Microsoft Security Essentials Installation Wizard
Error code:0x80070643

I also tried to install the Symantec Endpoint Protection as well but faced this error:
The system administrator has set policies to prevent this installation.

VMware Product Installation
The system administrator has set policies to prevent this installation.
OK
Some other antivirus has been installed in this PC without my knowledge, so I tried to trace or look for the installed antivirus so that I can uninstall them, but there weren’t any, so I take it that isn’t the problem.
Can somebody please give me some insights regarding this error?
Thanks so much.
