It works.. but i still don't really know what the problem was. Maybe the registry cleanup helped me out?
I created a new vs2010 solution including:
- Outlook Api
to get it all in one solution.
I also added a new class library "Extensibility" including the interface and enum files from IDTExtensibility2.cs.
Further more.. i did exclude the RibbonInterface.cs from the Project and used the NetOffice.OfficeApi.<interfaceName> instead (duplicated code?)
In VS2010 the libraries build platform target can be set to "any cpu". (not the executing lib due to registration problems)
Great work - thanks for your help!