Thorsten,
You are using VSTA v 1 correct? When I tried to pass a type (return typeof(int);) I got the message: "The constructor to deserialize an object of type 'System.RuntimeType' was not found."
This does not work in VSTA v 1- System.Type will not pass through the proxy layer.
This works in the VSTA v 2 beta release (I can send you sample code if you like).
What are you planning on doing with the type once it is passed to the proxy? If I have a better idea of what you're goal with this is I could suggest a work around for v 1 or do further testing with v 2.
>Are there benefits to change to VSTA CTP v2?
Between VSTA v 1 and VSTA v 2 the proxy changed dramatically- many things that didn't work in v 1 do work in v 2.
>I'm still using the .Net Framework 2.0 with Visual Studio 2005 and I expect some effort in switching to .Net 3.5, Studio 2008 and VSTA v2.
.Net 3.5 is a prereq- VSTA uses 3.5 assemblies. With Visual Studio 08 you can target the 2.0 framework instead of the 3.5 which would minimize the migration efforts. Also, Visual Studio 2008 is recommended but not required. You can opt to use Visual Studio 2005 instead- check out Using VSTA v 2 with Visual Studio 2005.