Hi
Could you please try this with v0.9999.2 of xetex?
\documentclass[a4paper,12pt]{article}
\usepackage{ptext}
\usepackage{fontspec}
\setmainfont[ExternalLocation,Script=Arabic]{HM_FTXsf}
\begin{document}
\ptext
\end{document}
it gives garbage output but had no problem with the previous version of
xetex in TeXLive 2012.
Note: HM_FTXsf is in texlive so you do not need to get it from CTAN.
However we are not the author of the font package.
--
Sincerely yours,
Persian TeX Group
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