Yes it is very frustrating - Technic is really, really flaky.
PC won't play Tekkit Lite; Mac won't run Tekkit Classic.
Mac, won't change to selected build.
Have cleared cache, using latest .jar version on Mac.
Nothing works and the myriad suggested solutions around the web don't do a thing.
All of this and Mojang still can't fix the basic Mac issue where you cannot drop a single item from a stack onto the crafting table, making the game all but unplayable for many people.
Macs seem to be basically an afterthought for just about anyone doing anything with Minecraft. Including Mojang.