Unable to connect to ST-Link

I'm new to Arduino. After install stm32duino, i tried to upload example blink code but received below messages

STM32 ST-LINK CLI v2.1.0
STM32 ST-LINK Command Line Interface

No target connected
Unable to connect to ST-LINK!

Anyone got solution for this? I tried to google it but no success :o :confused:

You'd probably do better on the stm32duino forum - as far as I can tell, most of the people here aren't using STM32duino - implying that the people who do have their own forum somewhere.