[XeTeX] (no subject)

[Alex Hamann]

I updated my Latex. Before I did it I had no trouble to run XeLaTex  
on a file with the following preamble:

\documentclass[12pt, oneside]{article}
\pagestyle{plain}
\usepackage{setspace}
\usepackage[applemac]{inputenc}
\usepackage[left=30mm,top=25mm,bottom=2cm,right=30mm]{geometry}
\usepackage[marginal]{footmisc}
\usepackage{fontspec}
\defaultfontfeatures{Mapping=tex-text}	\newfontinstance\fonta{Gentium}
%\newcommand\basetext{\fonta\fontsize{12}{14}\selectfont}
\usepackage{ucs}
\usepackage{sectsty}
\defaultfontfeatures{Mapping=tex-text}
\setromanfont[Scale=1.01]{Gentium}
\usepackage[sort&compress]{natbib}
\bibpunct{(}{)}{,}{a}{:}{,}
\bibliographystyle{plainnat}
\citestyle{}

\begin{document}
\doublespacing
\allsectionsfont{\mdseries\itshape\large}

\section{Introduction}

blablabla


Since I updated I get this Warning:

! LaTeX Error: Missing \begin{document}

Strangely, another file (different location on HD, different body,  
but same pramble) does not encounter this problem.

What is going on?

TIA, Alex