ok im gunna take a stab at this as my friend had the same problem, problem is you are downloading your setup files weather it be beta 1,beta 2 or 3 into the same folder, hence windows is adding an extension so all you need to do is rename the file bin -1(3)<<<<<<< and remove this (3), then retry the installer. make sure the same is done for the setup.exe aswell.
Make sure these two files are in a seperate folder.
Kind regards