DEV_TARGET_CMD_ERR is probably a hardware fault, mine was also caused by a problem at VDDA. I was using a cheap 32F103 breakout when the onboard regulator got fried and was outputing 5V. I though I had burned the processor because of that, I replaced it but had no luck. Turns out that while removing the burned regulator, I accidentally took out an inductor that connected VDDA to VCC and thus, it too was disconnected. After replacing it with a jumper wire, the processor got back to work.