[texhax] Problem with the xr-hyper package

[José Carlos Santos]

Hi all,

Six days ago, I posted this question at the comp.text.tex newsgroup, but 
I got no reply there.

Please consider these LaTeX files:

--------------------------- A.tex ---------------------------
\documentclass{book}
\usepackage{hyperref}
\newcommand*{\newchapter}[1]{\chapter[\texorpdfstring{\MakeUppercase{#1}}{#1}]{#1}}
\begin{document}
\newchapter{ABC}\label{cha}
A
\end{document}
-------------------------------------------------------------

--------------------------- B.tex ---------------------------
\documentclass[article]{memoir}
\usepackage{amsmath}
\usepackage{xr-hyper}
\usepackage{hyperref}
\externaldocument{A}
\begin{document}
\chapter{\nameref{cha}}
\end{document}
-------------------------------------------------------------

If I compile the file A.tex and then the file B.tex, I get this error 
message:

Runaway definition?
->\protect \protect {\<def>-command \i \<def>-command \j \<def>-command 
\ETC.
! TeX capacity exceeded, sorry [main memory size=8000000].

If the first line of the file B.tex gets replaced by 
\documentclass{book}, then I get another error message:

! Use of \@chapter doesn't match its definition.
\@uclclist ->\oe
                  \OE \o \O \ae \AE \dh \DH \dj \DJ \l \L \ng \NG \ss 
\SS \th...
l.7 \chapter{\nameref{cha}}

Why?

Best regards,

Jose Carlos Santos