Running LyX on Windows 7 with MiKTeX. I was trying to export LyX's "Embedded Objects tutorial" to PDF, but got this error:
Undefined control sequence
\hline
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.
The offending code seems to be
\let\myHlineC\hline
\renewcommand{\hline}
{\arrayrulecolor{red}\myHlineC\arrayrulecolor{black}}
(section 2.11.2 of the document).
May or may not be relevant: The document's preamble.