Thanks for the reply, but the "generate project" creates resx classes instead of windows form classes, moreover the code in the ".cs" classes is full of errors. Actually I had expected that the decompiler tried at least to separate the windows form classes in two partial classes as it should have been in the original project. Instead the VS generated code is together with the user implemented code in one class.
Even fixing the code of a small user control takes many hours. Fixing the whole code of all user controls and windows forms would take weeks if not months.