Unable to debug on custom STM32 board
Yestuday I have similar error and solve this problem. The main problem is the many people uses ST-Link Programmer/Debuger clone from Aliexpress. But this clone have no nReset signal pin, like in 15 pin of original ST-Link. There are only jReset & SWIM_Reset pins.
To solve the problem, I need connect Reset pin of target MCU to 18 pin (PB0) programmer MCU.