[OS X TeX] Microtype Fix (from: Microtype mystery)

[R. Vijay Krishna]

Hello:

Sorry to start a new thread, but my previous post seems to have been lost somewhere in the ether (I think).  This is about the microtype code that was posted earlier:

> the solution is to add the following lines after loading microtype:
> 
> \makeatletter
> \def\MT at register@subst at font{\MT at exp@one at n\MT at in@clist\font at name\MT at font@list
> \ifMT at inlist@\else\xdef\MT at font@list{\MT at font@list\font at name,}\fi}
> \makeatother

Unfortunately, this seems to conflict with something:  The following example 

-----------

\documentclass{article}


\usepackage{ifxetex}
\ifxetex

\usepackage[no-math]{fontspec}
\usepackage{xunicode}
\defaultfontfeatures{Mapping=tex-text,Scale=MatchLowercase}

\setmainfont[Mapping=tex-text,Numbers=OldStyle]{Adobe Garamond Pro}

\else
\usepackage[T1]{fontenc}
\usepackage{lmodern}

\usepackage[tracking=smallcaps,letterspace=30]{microtype}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%  Fix for Microtype %%  
\makeatletter
\def\MT at register@subst at font{\MT at exp@one at n\MT at in@clist\font at name \MT at font@list
\ifMT at inlist@\else\xdef\MT at font@list{\MT at font@list\font at name,}\fi} \makeatother
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\fi

\begin{document}

This is some filler text

\end{document}

---------

Running pdfLaTeX gives the desired output, however, compiling with XeTeX produces the following error:

-----------

! Too many }'s.
l.25 ...MT at font@list{\MT at font@list\font at name,}\fi}
                                                \makeatother
? 
! Extra \fi.
l.28 \fi

-----------

Getting rid of the fix for microtype solves the problem.  Is this a problem with ifxetex?  

Thanks,
Vijay.