Pixhawk connection issue with I2C plugged in

hi friends,

I have a strange issue with the Pixhawk 2.4.8

the Pixhawk board gets detected by the Win7 system and also by the Mission Planner when connected via the USB port.

but whenever I plug anything into the I2C port ( GPS / I2C Extender etc.) the Win7 machine gives error connecting to the Pixhawk board.

the USB gives a “Unknown Device” error and the Pixhawk board fails to get detected by the system.

what is causing this?