Solution: Do not use the version of Forge that comes from the installer. Use the Universal version.
I feel stupid having to ask this, but here I am. First modpack, fixed vanilla launch issue only to find this one. I click play, modpack begins loading, and then crash.
Technic Platform page for my modpack: http://www.technicpack.net/modpack/soft-landing.614416
Error on launch:
[b#283] Analytics Response [runModpack]: 200
[b#283] [16:56:09] [main/INFO]: Loading tweak class name cpw.mods.fml.common.launcher.FMLTweaker
[b#283] [16:56:09] [main/ERROR]: Unable to launch
[b#283] java.lang.ClassNotFoundException: cpw.mods.fml.common.launcher.FMLTweaker
[b#283] at java.net.URLClassLoader$1.run(Unknown Source) ~[?:1.8.0_31]
[b#283] at java.net.URLClassLoader$1.run(Unknown Source) ~[?:1.8.0_31]
[b#283] at java.security.AccessController.doPrivileged(Native Method) ~[?:1.8.0_31]
[b#283] at java.net.URLClassLoader.findClass(Unknown Source) ~[?:1.8.0_31]
[b#283] at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_31]
[b#283] at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) ~[?:1.8.0_31]
[b#283] at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_31]
[b#283] at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:106) ~[launchwrapper-1.11.jar:?]
[b#283] at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_31]
[b#283] at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_31]
[b#283] at java.lang.Class.forName0(Native Method) ~[?:1.8.0_31]
[b#283] at java.lang.Class.forName(Unknown Source) ~[?:1.8.0_31]
[b#283] at net.minecraft.launchwrapper.Launch.launch(Launch.java:98) [launchwrapper-1.11.jar:?]
[b#283] at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.11.jar:?]
[b#283] Java HotSpot 64-Bit Server VM warning: ignoring option MaxPermSize=128m; support was removed in 8.0