
If this happens then it is because the installer has failed to download and install the Microsoft HPC Pack 2008 R2 MS-MPI from the Microsoft website. To resolve you will need to download the MPI installer manually.
The installer gets MPI from:
64 Bit:http://download.microsoft.com/download/ ... pi_x64.msi
32 Bit:http://download.microsoft.com/download/ ... pi_x86.msi
Once installed the option to select 'On' and 'Max' will then be available.

Note: users with dual core processors will only see 'Off' or 'On', 'Max' will not be available.
