"Unable to make mpx file"

["Johannes Hüsing" <hannes@ruhrau.de>]

Greetings,

again, I am experiencing problems with MetaPost creating files with text
included.

The following is the contents of test-mpgraph.log after processing a file
calles test.tex:

This is MetaPost, Version 0.641 (Web2C 7.3.3.1) (mem=metafun 2002.4.10)  10 APR 2002 22:25
**test-mpgraph
(test-mpgraph.mp
{randomseed:=525}
write0 = `test-mpgraph.mpo'.

>> test-mpgraph.mp
>> test-mpgraph.mpx
! Unable to make mpx file.
l.90 label(btex
                Hallo wereld etex
The two files given above are one of your source files
and an auxiliary file I need to read to find out what your
btex..etex blocks mean. If you don't know why I had trouble,
try running it manually through MPto -tex, TeX, and DVItoMP.

This is what the source looks like:

\setupoutput[pdftex]
\mainlanguage[de]
\useencoding[win]

\runMPgraphicstrue
%\protectbufferstrue

%  Hack, um " nicht als active character zu definieren,
%  während Metapost bearbeitet wird
\appendtoks \let\handlecompoundcharacter\string \to \everyMPgraphic

\setupbodyfont
  [sansserif, 18pt]

\startMPinclusions
verbatimtex
\newif\ifloadfontfileonce
etex
\stopMPinclusions

\starttext

\startuseMPgraphic{beispiel}
label(btex Hallo wereld etex, origin);
\stopuseMPgraphic

\useMPgraphic{beispiel}

\stoptext

What could be the reason? 

Greetings

Johannes
-- 
Johannes Hüsing   There is something fascinating about science. One gets
hannes@ruhrau.de  such wholesale returns of conjecture from such a 
                  trifling investment of fact.                Mark Twain