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Looks like clearing the Java Cache was the issue here. I tried clearing Internet Explorer and Chrome cache, but that did nothing. Once I cleared Java cache, it worked like a charm. For those that have the problem, open Control Panel, then open the Java that shows up in CP. Under the General tab, click on settings then look in the lower right and click on Delete. Once that's done, try installing again. If that doesn't work, download the files manually and put them in the correct folders as posted above, then re-delete the Java cache and try again. Thanks Lex for the patience and guidance!! Edit: If you still want me to try the installer on 1.7 JVM, I can, but I think it may just be a problem with 1.8 cleans up code after a failed install in that it was probably a bad download in the beginning and 1.8 continued to use cached checksums regardless of new files with different checksums replacing the bad ones.

SHA1 for FML downloaded scala-compiler-2.10.2 21ac26a5434eb63bd93c1950e919cc80ff5ac226 SHA1 for FML downloaded scala-library-2.10.2 97a02a3f265b9608c33299d003a408b3560298f1 Manual D/L scala-compiler-2.10.2 64c8b1380cc53d6850823d6e4e7ae984aa44ef9c Manual D/L scala-library-2.10.2 6ba65d12cd09d441083262d6f73d2257fec7c663 So, the manual downloads are the correct version, but for some reason they are getting overwritten during the install process of Forge.

scala-library-2.10.2.jar as downloaded by FML is 702939B76217796BB8A8633C79CC78B3 scala-compiler-2.10.2.jar as downloaded by FML is BE208604479C64EA50FCFE8FEA8E1B13 Completely different from what that code shows. Edit: The MD5's for the ones you linked for manual download also don't match what's asked for in code.

Lex, Just thought I'd chime in on this as well. I was using 804 just fine and needed to update to at least 855. So, a few days ago, I downloaded 871 and came up with the same problem. I figured it was just a compile problem with that version so decided to wait a little bit before downloading a new version. I went on the website tonight and noticed that 871 is the last of the versions for 1.6.2, so I downloaded it again and came up with the same error. After some forum diving, I found the solution of manually adding those 2 files. I did and it's a no go. Even with those 2 files in the correct locations, FML installer still downloads and overwrites them with a different version. I can tell it's a different version as the file sizes aren't the same: FML Installer scala-library-2.10.2.jar 6,474KB Manual D/L scala-library-2.10.2.jar 6,955KB FML Installer scala-compiler-2.10.2.jar 12,963KB Manual D/L scala-library-2.10.2.jar 14,074KB I figure I better include java -version output: java version"1.8.0-ca" Java SE Runtime Environment (build 1.8.0-ca-b102) Java HotSpot64-Bit Server VM (build 25.0-b44, mixed mode) I have completely deleted and re-ran the Minecraft.exe launcher from Mojang and that still doesn't get rid of the problem.