WinUsbPy shows "No Usb devices connected" even when there are devices connected.

[Arvind Ram Prakash]

Hi,
I checked the code and the following line returned false and hence the "No Usb devices connected".

self.api.exec_function_setupapi(SetupDiGetDeviceInterfaceDetail, self.handle, byref(sp_device_interface_data), byref(sp_device_interface_detail_data), required_size, byref(required_size), byref(sp_device_info_data))

What could be the problem?