In this post, you’ll learn more about the Error ERROR_GRAPHICS_SPECIFIED_CHILD_ALREADY_CONNECTED – 0xC0262400 that is returned when working with the COM-based APIs in Win32
Win32 COM Error
ERROR_GRAPHICS_SPECIFIED_CHILD_ALREADY_CONNECTED – 0xC0262400
Win32 COM Error Error Description
Specified display adapter child device already has an external device connected to it.