[Libreoffice] Mono URE bootstrapping inside and outside web service

I am not sure whether this is the right place for a question like this, 
but I don't know any better place.

I have a small CSharp application which generates reports using 
Libreoffice. It has a small GTK interface and works without much 
problems on Ubuntu 11.04 with the bundled Libreoffice 3.3.2.

Now I would like to provide the same functionality over SOAP, so I 
created a WebService project. It uses the same libraries which contain 
the Libreoffice bootstrapping. The code can be found at 
http://pastebin.com/4u4mYRqG

When I run the WebService, it crashes at the location where I want to 
cast the object created by 
componentFactory.createInstanceWithContext("com.sun.star.frame.Desktop", 
context); with the message "Error: A type could not be loaded: 
unoidl.com.sun.star.frame.XComponentLoader".
The output is at http://pastebin.com/QQJEUR5A

The only idea I have about the differences between the two versions is, 
that the web service is maybe running a headless Libreoffice, and that 
could be causing the problem. The rest of the programs is quite the same 
concerning the Libreoffice connection.

Any ideas why this happens and how it can be corrected?

Greetings, Wolfgang.