AD FS 2.0 install on Server 2008 R2

I am attempting to install AD FS 2.0 on a 64-bit Server 2008 R2.
I've downloaded it from the MS Download Center, which states that Server 2008 R2 is one of the supported operating systems.

When I run the executable that's downloaded, I get and error message stating:

This AD FS 2.0 installtion requires the Windows Server 2008 SP2
operating system.

I found an MS page about the requirements of installing on Server 2008 and 2008 R2.
Here are some requirements that I've installed or are already installed:

• Windows Identity Foundation (WIF): Installed from the MS Download
  Center
• IIS 7: 7.5 is installed since it's a Server 2008 R2 machine.
• Windows Hotfix (KB981002): I followed the link that states I can
  download the hot fixes from here, but I get the message that the
  update is not applicable to my computer.
• .NET Framework 3.5 Service Pack 1: I have .Net 3.5.1 and 4.5.1 installed.

Is there something else that I need to install before the AD FS executable will work?

Any leads are appreciated.