On tekkit, whenever I try and go offline it says something like error applescript, but on multiplayer it's fine. How do i fix that?
The Tekkit modpack is designed for SMP use only. For SSP, you should use Technic. It's basically the same, but it's got a few more mods, the main one being Thaumcraft. If you use Technic Launcher, it's the one just above Tekkit.