Client> 2013-08-15 13:13:49 [sEVERE] [ForgeModLoader] Technical information: The class net.minecraft.client.ClientBrandRetriever should have been associated with the minecraft jar file, and should have returned us a valid, intact minecraft jar location. This did not work. Either you have modified the minecraft jar file (if so run the forge installer again), or you are using a base editing jar that is changing this class (and likely others too). If you REALLY want to run minecraft in this configuration, add the flag -Dfml.ignoreInvalidMinecraftCertificates=true to the 'JVM settings' in your launcher profile.
Try running vanilla 1.6.2 then re running the installer, else really go check if there is something else in the jar that shouldnt be there.