During the Setup Lync Server Components step of the Lync 2010 Server System installation, if the setup fails with the error: "Prerequisite installation failed: Wmf2008R2".

Run the following in an elevated command prompt:
%systemroot%\system32\dism.exe /online /add-package /packagepath:%windir%\servicing\Packages\Microsoft-Windows-Media-Format-Package~31bf3856ad364e35~amd64~~6.1.7601.17514.mum /ignorecheck

This command will install the Windows Media Format Runtime. All Front End Servers and Standard Edition servers with the conferencing feature deployed must have the Windows Media Format Runtime installed. WMF is required to run Windows Media Audio (.wma) files that the Call Park, Announcement, and Response Group applications play for announcements and music.

Here is another resource showing this issue: http://www.expta.com/2011/05/lync-server-2010-installation-fails.html