I tried several times to play with XeLaTeX (being used to "classical" LaTeX) but since I installed MacTeX 2011 and updated it with TeX Live Utility, I got that kind message :
(/usr/local/texlive/2011/texmf-dist/tex/latex/l3packages/xparse/xparse.sty
/usr/local/texlive/2011/texmf-dist/tex/latex/l3packages/xparse/xparse.sty:57: U
ndefined control sequence.
<argument> \ExplFileName
l.57 ...e}{\ExplFileVersion}{\ExplFileDescription}
If I continuously press "Return", I got a lot of error messages linked to Unicode font scripts, for instance :
/usr/local/texlive/2011/texmf-dist/tex/latex/fontspec/fontspec.sty:1909: Undefi
ned control sequence.
l.1909 \newfontlanguage{Efik}{EFI}\newfontlanguage
{Greek}{ELL}
I seems there is a problem between version of xparse, fontspec etc. But it occurs even after re-installing Tex Live and updating only one package not linked to xelatex or fonts. The log file is quite long with all these errors (about 4200 lines).
Could it be caused by the scripts run by tlmgr after updating a package?
Edit:Sorry for mistake about "answer".
Here is a link to the log file : http://dl.dropbox.com/u/6420461/xelatex3.log
l3kernel
does not match that forl3packages
. Try at the Terminalsudo tlmgr update l3kernel
andsudo tlmgr update l3packages
.