Not really sure this is your bug, but I got a StackOverflowError due to infinite recursion in worldgen when using Vazkii's Garden of Glass (from curseforge) with Botania.

Here's the crash report:
http://pastebin.com/Q3AEW0VL

looks more like thaumcraft's fault. Can you check if it fails without it?

Not Thaumcraft. Turns out it was ShadowTweaks.

Cool, thanks for tracking it down. Might wanna report if not already done so (though I already poked him on IRC about it)