You may have problems installing UcmaRedist.msi (the Microsoft Office Communications Server 2007 R2, Microsoft Unified Communications Managed API 2.0 Core Redist 64-bit) on Windows Server 2008 or 2008 R2. I ran across this myself when installing the Microsoft Office Communications 2007 R2 Web Service Provider for Lync Server 2010.
You receive the following error:
Microsoft Office Communications Server 2007 R2, Microsoft Unified Communications Managed API 2.0 Core Redist 64-bit installation requires Microsoft .NET Framework 3.5. Installation can not continue.This happens if you have the .NET Framework 4.0 installed. Uninstall the Microsoft .NET Framework 4 Extended and then the Microsoft .NET Framework 4 Client Profile components from Control Panel > Programs and Features. Then restart the server and install UcmaRedist.msi. 7:29 PM