Always install Exchange 2010 rollups from an elevated command shell
If you simply double-click on an Exchange 2010 rollup package to install, as the installation instructions tell you to, it will prompt for elevation. Grant it, and it will appear to install correctly. However, you may soon find that your Outlook Web Access is tanked.
Always launch the rollup installer from an elevated command shell, by right-clicking on the Cmd or PowerShell shortcut (depending on which one you’re using) and selecting Run as Administrator.
If you’ve already run it the normal way and your OWA is currently a steaming pile of wreckage, simply run the rollup again from the elevated shell, and it should be working after the second install.
This was widely reported with rollup 1 and is definitely still a problem with rollup 2. Perhaps with rollup 3, Microsoft will actually document the correct install procedure.