I've got a webbrowser control and have implemented IDocHostUIHandler using err.raise E_NOTIMPL for events not handled (events like TranslateURL for example).

The code works fine on a Windows 7 32bit machine but not on Windows 10 64bit. As soon as the code hits the err.raise E_NOTIMPL I get the error 445. It's not clear to me which object the error message refers to (the err object?!).

Possible clues:

* Only occurs in dev mode

* If I block out the err.raise in dev mode the webbrowser control does not accept keyboard input (though one can paste into the control so the webbrowser is clearly in edit mode)

* Compiled everything works fine - I can type into webbrowser control etc.

Any guidance would be much appreciated!

Tom