The problem is, I think, not related to umlaud characters, but to robots.txt
restrictions. 

I'm currently mirroring the /Schätztheorie page  with no problems so far.  

The robots.txt at <http://mars.wiwi.hu-berlin.de/robots.txt> disallows
mirroring/indexing by all user-agents:

User-Agent: *
Disallow: /

See this posting for info about robots.txt rules: 
<http://forum.httrack.com/readmsg/16428/16426/index.html>

- Bo Hovgaard Thomasen