sp614x

It looks like the OptiFine Tweaker is being loaded after the deobfuscation step and is of course crashing because it uses obfuscated class names. The JAR Tweaker support was added by cpw specially to enable OptiFine dynamic loading and using the obfuscated class names was and still is a fixed requirement for that. The solution would be to load the JAR tweakers before deobfuscation (as it was in 1.6.2) or to split the loading of obfuscated and deobfuscated tweakers (if needed at all). Updating OptiFine to use unobfuscated classes is not possible, because it should also run without Forge being present.