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Do you still have the last .bin and .exe files somewhere (the ones the Downloader downloaded)? If so, please send me a PM with the exact filesizes of these ones and the ones you got from the website.

As for the problem, it may be a file hosting issue - I will put a request to purge these files from our file hosting provider's cache just in case.

It's also possible that some overzealous anti-virus program finds a false positive in the Launcher and doesn't allow you to install it, perhaps even without your knowledge. If redownloading the files doesn't help, try disabling your AV software for the duration of the installation.