Memoir class and Bibtex

Memoir class and Bibtex

I have
biblio.bib:
@article{XX,
title={{Title}},
author={Author},
journal={Journal Title},
volume=1,
number=11,
pages={1-2},
year=1666
}
And myfile.tex
\documentclass[oneside]{memoir}
\usepackage{natbib}
\begin{document}
...
\cite{XX}
...
\bibliography{biblio}
\bibliographystyle{acm}
\end{document}
I get the error:
ERROR: Class memoir Error: Font command \sc is not supported.
--- TeX said ---
See the memoir class documentation for explanation.
Type H <return> for immediate help.
...
l.4 {\sc
Author}.
--- HELP ---
From the .log file...
Use \textsc, or \scshape{...}, or the oldfontcommands option
What might I be doing wrong?