I've "successfully" installed Forge using the recommended 1.6.4 Forge installer .jar from the files page. However, when I select the Forge Profile in the profiles list and attempt to run Minecraft in Magic Launcher I get the following error:

 

 

*** MagicMinecraftLauncher 1.1.7 ***

  LCP: C:\Users\Matt\SkyDrive\Minecraft\Mods\OptiFine_1.6.4_HD_U_C5.jar;C:\Users\Matt\AppData\Roaming\.minecraft\versions\1.6.4-Forge9.11.1.916\1.6.4-Forge9.11.1.916.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\net\minecraftforge\minecraftforge\9.11.1.916\minecraftforge-9.11.1.916.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\net\minecraft\launchwrapper\1.8\launchwrapper-1.8.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\org\ow2\asm\asm-all\4.1\asm-all-4.1.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-library\2.10.2\scala-library-2.10.2.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\org\scala-lang\scala-compiler\2.10.2\scala-compiler-2.10.2.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\lzma\lzma\0.0.1\lzma-0.0.1.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\net\sf\jopt-simple\jopt-simple\4.5\jopt-simple-4.5.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\com\paulscode\codecjorbis\20101023\codecjorbis-20101023.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\com\paulscode\codecwav\20101023\codecwav-20101023.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\com\paulscode\libraryjavasound\20101123\libraryjavasound-20101123.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\com\paulscode\librarylwjglopenal\20100824\librarylwjglopenal-20100824.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\com\paulscode\soundsystem\20120107\soundsystem-20120107.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\argo\argo\2.25_fixed\argo-2.25_fixed.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\org\bouncycastle\bcprov-jdk15on\1.47\bcprov-jdk15on-1.47.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\com\google\guava\guava\14.0\guava-14.0.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\org\apache\commons\commons-lang3\3.1\commons-lang3-3.1.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\commons-io\commons-io\2.4\commons-io-2.4.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\net\java\jinput\jinput\2.0.5\jinput-2.0.5.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\net\java\jutils\jutils\1.0.0\jutils-1.0.0.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\com\google\code\gson\gson\2.2.2\gson-2.2.2.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\org\lwjgl\lwjgl\lwjgl\2.9.0\lwjgl-2.9.0.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\org\lwjgl\lwjgl\lwjgl_util\2.9.0\lwjgl_util-2.9.0.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\org\lwjgl\lwjgl\lwjgl-platform\2.9.0\lwjgl-platform-2.9.0-natives-windows.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\org\lwjgl\lwjgl\lwjgl\2.9.1-nightly-20130708-debug3\lwjgl-2.9.1-nightly-20130708-debug3.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\org\lwjgl\lwjgl\lwjgl_util\2.9.1-nightly-20130708-debug3\lwjgl_util-2.9.1-nightly-20130708-debug3.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\org\lwjgl\lwjgl\lwjgl-platform\2.9.1-nightly-20130708-debug3\lwjgl-platform-2.9.1-nightly-20130708-debug3-natives-windows.jar;C:\Users\Matt\AppData\Roaming\.minecraft\libraries\net\java\jinput\jinput-platform\2.0.5\jinput-platform-2.0.5-natives-windows.jar

  WindowMaximized: true

  MainClass: net.minecraft.launchwrapper.Launch

java.lang.ClassNotFoundException: net.minecraft.launchwrapper.Launch

    at java.net.URLClassLoader$1.run(Unknown Source)

    at java.net.URLClassLoader$1.run(Unknown Source)

    at java.security.AccessController.doPrivileged(Native Method)

    at java.net.URLClassLoader.findClass(Unknown Source)

    at java.lang.ClassLoader.loadClass(Unknown Source)

    at java.lang.ClassLoader.loadClass(Unknown Source)

    at magic.launcher.Launcher.main(Unknown Source)

 

 

 

I've come across this exception every time I attempt to install Forge and run it with Magic Launcher. The solution I've found is to first run it in the default launcher minecraft.exe file. And then run it in Magic Launcher. I was curious why this would be necessary, so I am asking here. Any ideas?

That's interesting, I have two ideas. One, somethings wrong in the .json file that launching it normally can fix it. Two, Forge may require launching vanilla in order to install some sort of important file in your .minecraft folder. Also, MagicLaunher has flaws, which can cause issues, considering that that error means the launch command failed, or something is missing/wrong in your class path. At least your Forge is functional, right?

Run modded mc at least once through the vanilla launcher.