Several other users reported the same problem that you've encountered. It depends of the location of the source file. If the source file is on your local machine, then it is possible that you have previously installed some other codec packs and you are liable to load conflicting codecs or possibly even malware, and for these resasons you should avoid loading them at all. Make sure you have installed the .NET Framework 4, and that you have the latest version of Freemake Video Converter. If this doesn't help you, try converting the MP4 file to AVI and then the resulted AVI file to WMV.
If the file is hosted on the Internet, then you should use the Paste URL button located in the top-right section of the program's window instead of downloading it and trying to convert it. If you get the same result, you should check your Internet connection, because conversion failure has been reported due to unstable Internet connection.
If none of this helps, you might want to do a System Restore back to when your system was stable.