OK, I figured this out. It wasn't every modpack, just the first six or seven that I tried. I realize, of course, that the error message I'm getting says to report it to the modpack author, but when there's so much link rot going on, can you blame me for thinking it might be the launcher? Options for fixing this: How do I even report this to the various and sundry modpack authors? There's no clear mechanism. Add a "report linkrot" button somewhere. If enough users press it, drop or preferably flag the modpack. Automate linkrot checking. Probably ought to only drop modpacks which fail 3 consecutive tests, with an appropriate notice to the modpack author. Also probably should STOP this test if we're getting numerous fails, as this probably indicates that some major hosting service *cough*dropbox*cough* has made changes and it'll be better handled with admin intervention. separate issue: Is there any way to search for modpacks which contain and *do not* contain specific mods? I hate NEI, and want customOreGen and a couple others. Alternately, is there a quick and easy way to drop my desired mods into a folder and then launch vanilla or something? The only way I've found to figure out what mods a modpack contains is to install the damn thing and check the mods directory. Given that, downloading and configuring the specific mods I want is probably faster. But then what's the point of the launcher? I'd apologize for posting this despite not having a bug, but when I've already completed the lengthy registration process (WTF kinda question is "What Technic modpack is about adventure and spells?" anyway? I've still got NO idea. And if "zombies" aren't what drops rotten flesh, then it beats the heck outa me!) and mostly composed the question before I figure it out, it probably ought to be reported anyway.