Check out Mac unable to install OS X 10.8.2
If you own one of Apple’s latest 2012 Mac Mini systems and are attempting to update it to the latest version of OS X, you may find the update is not available via the App Store’s Software Update service. Furthermore, if you download the manual updater for 10.8.2 and attempt to install it, you will see an error that states: “Error: OS X Update can’t be installed on this disk. This volume does not meet the requirements for this update.”
The reason for this error is the 2012 Mac Mini requires a special version of the 10.8.2 update, which Apple pulled from the App Store last Friday and has not yet released a new one.
Detaits of Mac mini
While some have speculated Apple may have pulled the update for the upcoming 10.8.3 release, while Apple has removed prior versions of OS X such as OS X Lion from the App Store after Mountain Lion was released, this is very unlikely as the new release is not yet available and is still under testing. Furthermore, Apple still maintains update packages so older versions of OS X can still be updated to their latest versions.
Apple has not issued an explanation as to why the update was pulled, but it is more likely because of a glitch in the updater or a problem with the App Store, and the update will likely be reissued soon once the problem is fixed. However, until this happens, affected users will be at a small disadvantage because they will not be able to install other recent software updates that requires OS X 10.8.2 such as those for iPhoto and Aperture.
If you have a 2012 Mac Mini system and the OS X 10.8.2 update is not showing up in your Software Update list, then for now the only option is to wait. Do not try to install the manual delta or combo updaters that are available online, as these will not work and will instead result in an error. Hopefully Apple will address the problem ASAP and allow Mac Mini users to get the latest version of OS X.
source – cnet