I'm slowly nearing the problem. If I uncheck the header-footer merge the error goes away.
I have isolated the header-footer into it's own report, but I cannot reproduce the error. I'm guessing it has something with the merge to do. I don't have more time right now. Will get back to this if you need more input.
My header-footer goes all the way to the edge of the paper. I.e. no margin. Here is how the header looks.