I Do not Have Administrative Privileges in an Administrator Account

This is my home desktop computer running with Windows XP Pro. I have just two user Accounts on this and both are Administrators. Yesterday I was trying to run Windows Update but that ended saying:

“Error code 0x8ddd0002
To install updates from this website, you must be logged on as an administrator or a member of the Administrators group on your computer. If you use Windows XP, you can see if you are an administrator by going to User Accounts in Control Panel.”

Surprisingly I got such Admin error earlier also while installing a game on this computer. Am sure I am Admin of this PC but still checked it thrice again in control panel. Then why this problem occurs? Any idea how can get it solved?

There might be some specific registry keys or folders that might not having Admin permissions in your account hence you getting that error. Anyways, I found a KB Article describing exactly the same problem. You must check it:

You receive an "Administrators only" error message when you try to visit the Windows Update Web site or the Microsoft Update Web site

Thanks a lot for the help RaAbi.

I tried everything mentioned on that article but that dint helped. Can you please provide some other solution?