.jar files "package unavailable"

[AnthemXI]

I've recently tried to install forge for Minecraft but upon attempting to open the .jar file, I was met with "package unavailable". I then tried to reinstall the latest version of Java and the problems persisted. I've also tried to open other .jar files and they are unavailable. When trying to open them with WinRAR and the command prompt; No luck.

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