I understand that my question is a duplicate of one that seems to have resolved itself quite some time ago. However, that particular thread did not post the steps they went about to fix said issue. Basically, what's happening is this. I start the FTB launcher, choose Horizons, choose Recommended Version, launch the game, wait forever to download the mod pack, and wind up in version 1.6.4 of Minecraft, which is not compatible with the server. I am running 32 bit Puppy Linux, FTBlaunch 1.4.7 . The newest version of Horizons the launcher gives me access to is 2.1.1 . I am willing to try things, and I will document whatever solution I come to.