[AUCTeX] Multifile pb: C-c C-c RET (that is latex) doesnot work

[zell08v]

Hello everyone, 

I am a newbie to Auctex. My problem is about multifile with Auctex + Emacs.
Anyone can explain me why the following does not work when I tape C-c C-c RET
from _part.tex. Thank you for your ideas. 

-----------------Here is the source file _main.tex----------------
\documentclass{article}

\begin{document}
Hello this is the main part.
\input{_part}
\end{document}

-------------- Here is the source file _part.tex------------------

Hello

%%% Local Variables:
%%% TeX-master: "_main"
%%% End: