After experiencing tons of weird LaTeX errors, and reading this:
http://www.tex.ac.uk/cgi-bin/texfaq2html?label=erroradvice, I found that
the use of scrheadings was responsible for the weird behaviour.
I rewrote the preamble and fine-combed my ERT parts, and finally all
traces of scrheadings were gone. So I can produce output again now.
What happened is this: scrheadings seems to affect the calculation of
typearea, and as a result, I had "! Latex error: Float(s) lost".
I don't really understand that, but hey, the problem wasn't related to
LyX and I solved it, so what the heck.
Hope this is useful for anyone experiencing similar problems.
-- Christian