you can fall through coplanars as well..Wich is ,if its alot of them,a pain in the ass to fix.Thougt there is diffferent fixes like


First go Editable poly,then pick the two vertecies that causes the coplanar,then simply press the button "Make planar".OBS! this can move other faces around but that rarely happens..This is a fast way to do it whitout messing up your model.

Its just a temporaly fix and can screw up some faces so dont use it to much:P

As for the other error is if you have created faces wrong..I suggest start to look over the map again.Or start fix the coplanars atleast.