WillAndPrime

If you get a gray screen when you start the game that means that you did one of these, or both of them: 1) You have the wrong version of optifine (It is Optifine 1.4.6 for Tekkit Lite 0.6.5) 2) You put optifine in the minecraft.jar instead of the modpack.jar If you still are having problems with the gray screen, then try deleting the META-INF from inside the modpack.jar Only do this if you have backed up your modpack.jar and have already tried steps 1 and 2.