I'm getting a download error when trying to download 1.2.0. What versions of waila and NEI were in 1.2.0? I'll just manually add them in.
Edit 1: First trying with only NEI version 1.0.3.74 and not touching waila. I've stopped crashing, but NEI still is not functional. It now only shows 4 rows of items, from various mods with no similar names.
Edit 2: Downgraded Waila to 1.5.6a and getting the same issue as above. Still 4 rows of items, but most of the items are different this time. Aside from a bunch of mariculture fish, they've appeared both times.
Edit 3: Downgraded NEI again to 1.0.3.67. Same result.
Edit 4: Decided to try a new world to see if the problem was somehow connected to my current world and crashed on loading the word twice in a row. Appears to be something wrong with the buildcraft API.
Crashlog:
http://pastebin.com/kVSHGc6W