Hmm I had to try a couple times, but it finally said "try install again using recommended settings" whatever the hell that means....Seems to work now. Also, what is this new warning they give before downloading it?
I've got the Castle Link on Windows 7 64-bit - downloaded the Castle Link, filled in my details, Firefox downloaded it, I ran the file, it worked. I'm not sure what warning message you are referring to, unless you still have the user access restrictions/verification running?
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This has made a lot of people very angry and has been widely regarded as a bad move.