could be anything, really. did you tighten bolts in a pattern? I start all the bolts in loosely by hand, first. If there isn't a specified tightening sequence, when I begin to put torque to them I start with the innermost, and work side to side, and outward in a criss-cross pattern.
if you didn't use the cork gaskets for the ends, I'd use something to measure the gap between the "china" walls and the bottom of the ends of the intake. If it is more than 1/2 the thickness of an uncompressed cork end gasket, but less than the uncompressed thickness, then I would consider using the cork gasket, IF the manifold locating pins are still intact. If you are not using the pins, then you have to solidly glue those gaskets to the "china" wall, first, so they don't pooch in or out, when you start drawing the manifold down.This can happen if you put "wet" rtv on BOTH sides when you assemble it because the gaskets are somewhat slippery until the rtv cures.
