In my experience Updates can take a few seconds/minutes to become available because PS needs to contact Adobe servers before it shows as enabled.
You can also download the current update to ACR from this page:
You will need to be running Windows 7 or OSX 10.7 or newer for this version of ACR.
If the menu item itself is grayed out, that probably points to a trial version of the software or to a hacked, pirated copy.
Thanks ssprengel Perfect
Sorry if I answer only now, but I was busy
Now I can work with the files of my new Canon 5d MarkIII