If you’ve never seen this error code before when installing Update Rollups for Exchange 2010, then you haven’t lived. There’s plenty of blogs and articles out there about it, but I wanted to record it for my own purposes so I don’t go trawling for the answer next time!
In a nutshell, the reason this happens is that UAC hates you.
Simple fix to this is to run CMD as Administrator, and use msiexec to install the Update Rollup, like this:
msiexec /update Exchange2010-KB2961522-x64-en.msp
Gotchas? Well the file should be on a local drive (not a network share). If you are still having problems after this, take a gander at the following KB article: http://support.microsoft.com/en-us/kb/2784788/en-us
That’s about it. Happy Update Rollup’ing!