As far as I know there is no previous version of the VSO Service Credentials Viewer available for download any more. I am surprised that installing
Visual Studio 2015 Preview did not help you. The only other prerequisite stated on the site of the vendor is .Net 4.5. Can you please double-check if you really have .Net 4.5 on you machine (the installer of VSO Service Credentials Viewer
takes care of installing it, but just in case ...). Besides that I am afraid that for now I cannot suggest another option but contacting naked ALM, as you already mentioned, to figure-out what could be the reason for the tool not to be working on your side.
Let us know if we can assist you with something else.