User1564952282 posted
Ok, I found the solution to this problem myself.
It appears that before you can issue the GetResponse the stream that was used to write the request (here oWriter) must be Closed. This is different behaviour than on the desktop environment.
I found that out by making the real message of the exception available. This message was not available as a result of a not deployed diagnostics cab file:
C:\Program Files\Microsoft.NET\SDK\CompactFramework\v2.0\WindowsCE\Diagnostics and choose the file for your language.
Thanks for all the answers [:D]
Jan