Sections and dimensions problem, solved.

I had a bent part with a cut across the angled portion, and used a favorite hack to make a partial auxiliary view - a partial section view with a line that doesn't cross the part. Dimensions parallel to the section line wouldn't come up with the sketched section line made parallel with the part edge, and I couldn't put the section line in the sketch plane. Making the section line parallel with the sketch plane solved the problem.