Use correctly the GetOpenFileName function.
Use _lcreat instead of _lopen to create a new file.

Use get_parameter to read the three parameters to RegisterOCX.
Remove the ERRs and TRACEs now that we return the HRESULT.

Turn off updating for that the unselect and select and then turns it
on for the focus call, this results in 1 edit notify being sent at the
end of the operation.