While installing Modernization Workbench on Windows Server 2008 R2 64 bit, .net 3.5 installation fails with error asking to use Role Management Tool to install.

Go to Microsoft Management Console (from Start/Run/mmc), go into Roles and apply .Net 3.5 that was pre-installed (it just has to be activated). Once the .Net installation is activated and installed then running Setup.exe will do the installs for Licence and MWB.