Debugger - Cortex-M Error

I get this message error when I click "Run" in debug session:

Debugger - Cortex-M Error
Cannot access de target.
Shutting down debug session.

the program worked before, and I tried changing the ST-Link, upgrading the firmware of the ST-Link and changing the microcontroller (STM32F103C8T6).

I generated the configuration with STM32CubeMX and the "useful" code is next

/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "stm32f1xx_hal.h"

/* USER CODE BEGIN Includes */
#define PERIOD 6400
/* USER CODE END Includes */

/* Private variables ---------------------------------------------------------*/
ADC_HandleTypeDef hadc1;

TIM_HandleTypeDef htim4;

/* USER CODE BEGIN PV */
/* Private variables ---------------------------------------------------------*/
volatile uint16_t adc_value;
/* USER CODE END PV */

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
void Error_Handler(void);
static void MX_GPIO_Init(void);
static void MX_TIM4_Init(void);
static void MX_ADC1_Init(void);

void HAL_TIM_MspPostInit(TIM_HandleTypeDef *htim);


/* USER CODE BEGIN PFP */
/* Private function prototypes -----------------------------------------------*/

/* USER CODE END PFP */

/* USER CODE BEGIN 0 */

/* USER CODE END 0 */

int main(void)
{

  /* USER CODE BEGIN 1 */

  /* USER CODE END 1 */

  /* MCU Configuration----------------------------------------------------------*/

  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();

  /* Configure the system clock */
  SystemClock_Config();

  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_TIM4_Init();
  MX_ADC1_Init();

  /* USER CODE BEGIN 2 */
        HAL_TIM_PWM_Start(&htim4, TIM_CHANNEL_1);
        HAL_ADC_Start_DMA(&hadc1, (uint32_t*) &adc_value, 1);
  /* USER CODE END 2 */

  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
  /* USER CODE END WHILE */

  /* USER CODE BEGIN 3 */
                TIM4->CCR1 = (PERIOD/4096)*adc_value;
  }
  /* USER CODE END 3 */

}
/********************************************/
// Configuration down here