Strange behaviour on Windows 2008 Stanard vs. Windows 2008 R2

[twinpeak]

I have deployed a webservice and a testclient on a windows 2008 R2 server for testing purposes. In this scenario all works fine

But when I install the same webservice and testclient on a Windows 2008 Standard (not R2) server, it behaves in a completely different way.

The configuration of IIS is as far as I can see identical


Has anyone else experienced this?