The devolper sp614x of the mod OptiFine just announced on twitter that he updated the OptiFine D1 for 1.6.4 version and this version should now be compatible with the 1.6.4 FTB mod packs. How to install? Download the version OptiFine D1 for 1.6.4 from here [1.7.4] OptiFine HD D1 (FPS Boost, HD Textures, AA, AF and much more) - Minecraft Forum Open your FTB Luancher and click on "Edit Mod Pack" Click on "Add Mod" and select the downloaded Optifine jar Close the window and luanch your mod pack. Done!
