It seems that mediafire is hosting a bad copy of your rarfile, whenever I download and extract it (no matter how many times nor where it is saved from) the executable returns an windows error box that says "MorroblivionInstaller.exe is not a valid Win32 Application."
I probably should have stated
I probably should have stated this already, but I both have .NET 4 as well as could previously run the previous installer fine. (although just to be safe, I ran a reapir on .NET 4 and restarted my computer and tried running it again... no dice.)
Sent a message to mediafire
Sent a message to mediafire about the file, they restarted the server hosting the file and it appears to have been remedied.
Try getting the most recent
Try getting the most recent version of .NET which is required to run the installer.
https://www.microsoft.com/net/download.aspx