I know this is a fairly old topic, but I'd like to point out this is happening to me and I doubt it's my system. I can run other 128x texture packs without much issue. In fact, I can run SPHax 128x perfectly fine, in addition to some others. However, when I switch to Minecraft Enhanced 128x - it won't load. Any explanation for that? SPHax is a rather hefty texture pack...
Mine selects the pack and shows that it is using it, but it loads the default textures. I even checked the "options" file, and it said it was using the pack. And not just on the high res ones, even does it on 16x16.
128x Texture packs won't work?