Exchange 2013 Installation Failure step 7

I am installing exchange 2013 on a Server 2008 R2 DC -

installation runs perfectly up to step 7 ( Management tools) then i receive this error

'Error:
The following error was generated when "$error.Clear();
          Copy-Item -Path ($RoleInstallPath+"Bin\mmc.exe.config") -Destination (Split-Path (where.exe mmc)) -Force
        " was run: "The term 'where.exe' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again.".'

is this a simple fix? if so how can i do it? iv never seen this before and cannot find anything on our lovely friend Google.

Thank you