This is occuring because of the underscore in the domain of the site. Windows allows this, but it against RFC (its not explicit about underscores directly -- that I can find), see the wikipedia page on this http://en.wikipedia.org/wiki/Hostname, the RFC on choosing a hostname doesnt explicitly mention underscores http://tools.ietf.org/html/rfc1178
If you would like to allow it you can add a /etc/hosts file entry for the site.
Thanks for the reply.
I''l try to edit the file with WinSCP or Putty.
Do I have to do someting special within the configuration of the webgateway?