Finding source of pdflatex build error

[Rich Shepard]

I've a large report, six large chapters, bibliography, two appendices.

When I try to compile it I get an error. Trying to find where that error is
created, I made a new, empty mwe.lyx file.

Starting at the bottom of my report, I copied the appendices and
bibliography to mwe.lyx. Saved and built. No error. I then added chapters
individually to mwe.lyx, saved and built. No errors. Continued up through
Chapter 2; didn't add Chapter 1 because the report had no issues before I
added text, citations, and the appendices.

So, somewhere in what I added today pdflatex couldn't digest. But, copying
from the end of the report forward, chapter-by-chapter everything builds.

What other procedure should I use to find what's causing the error?

Rich