I have problem displaying the author name in citation when using natbib. I wrote
This is explained in \citeauthor{lamport94}, and what I get is:

, and my entire code is given by:
\documentclass[english]{article}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\makeatletter
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% User specified LaTeX commands.
\PassOptionsToPackage{square,numbers}{natbib}
\usepackage{natbib}
\makeatother
\usepackage{babel}
\begin{document}
This is explained in \citeauthor{lamport94}.
\begin{thebibliography}{9}
\bibitem{lamport94} Leslie Lamport, \emph{\LaTeX: A Document Preparation System}. Addison Wesley, Massachusetts, 2nd Edition, 1994.
\end{thebibliography}
\end{document}
I wonder what is wrong?
Note:
I'm using LyX.
I'm aware of thread Author not appearing, but there's no resolution there, and I use \citeauthor{} insteand of \citet{}.
