Windows upgrade to 8.1 needs admin privilegies

I've found in those days a problem with my original copy of Windows 8.
From Windows store I have a notifications that informs me that update to 8.1 is available.
Ok, let's do this update.
But when I click on "Update" a message tells me that I have no administrator privileges.
WTF?! I am the only user and I have all permissions.
I check it from preferences and from command-line and I am really an administrator user.
So, what's the problem?

After long search and long try-and-try I've discovered a solution.
The problem is the windows update KB2871389.
To solve this, from control panel -> installed update remove that and reboot.
After that, clear store cache launching WSRESET.exe.
Then, back to windows update panel, in settings, and force all updates available.
Finally, go to the store and do normally the update to 8.1. Now it should works!!