Generating interop wrapper classes throws error

When generating interop wrapper classes in visual studio 10 the tool throws the following error: Interopform wrapper class generator: Error creating interopF开发者_Python百科orm Wrapper Classes for Project xxx

Error list is empty

where can I start to search for the source of the Error?

The issue here was: moving the interopform into a folder. Interopforms can only be in the root of the containing project to generate a wrapper class.