If you've tried running on a Windows 2008 R2 the RU3 Microsoft Exchange 2010 SP1, you have probably encountered a installation problem.
To learn more you must enable a registry key that can generate installation logs. To do this edit the following registry key:
HKEY_LOCAL_MACHINE \ Software \ Policies \ Microsoft \ Windows \ Installer
Ps: if the folder "Install" does not exist create it.
Then restart the install process to diagnose the problem more advanced. If you look closely you should find the installation log very detailed the following exception:
CAQuietExec: You must have administrative credentials to perform this task. Contact your system administrator for assistance.
To complete the installation of this patch, open a command prompt as administrator and run the patch from the command line. The program will install properly.