NRF_SERIAL_EVENT_DRV_ERR, what is the cause?

Question

Hi, 
 I'm trying to receive data from a UART transceiver. I'm using a nRF52 DK with a RS485 to UART transceiver chip. 
 On my debug session I get the " NRF_SERIAL_EVENT_DRV_ERR" in the serial event handler. 
 My serial settings are correct because I get correct data on a serial monitor. 
 I have attached the relevant code: 
 void init_rs485()
{
	NRF_LOG_DEBUG("init_rs485");
	// Init the Serial UART0 for IPN
	ret_code_t ret;
	ret = nrf_serial_init(&serial1_uart, &m_uart1_drv_config, &serial1_config);
	APP_ERROR_CHECK(ret);
}

void serial_event_handler(struct nrf_serial_s const * p_serial,
 nrf_serial_event_t event)
{
	ret_code_t ret;
	char c;
	switch (event)
 {
 case NRF_SERIAL_EVENT_TX_DONE:
 break;
 case NRF_SERIAL_EVENT_RX_DATA:
 //NRF_LOG_DEBUG("in serial_event_handler...");
 //Read one char from queue at a time
 do{
 ret = nrf_queue_read(p_serial->p_ctx->p_config->p_queues->p_rxq, &c, sizeof(c));
 if (ret == NRF_SUCCESS) {
 //Echo char back to port
 NRF_LOG_DEBUG("%x ", c);
 ipn_process_event_byte(c);
 }
 } while(ret == NRF_SUCCESS);
 break;
 case NRF_SERIAL_EVENT_DRV_ERR:
 NRF_LOG_ERROR("in serial_event_handler %x", event);
 static uint8_t error_ctr = 0;
 if(error_ctr++ > 5)
 sd_nvic_SystemReset();
 break;
 case NRF_SERIAL_EVENT_FIFO_ERR:
 NRF_LOG_ERROR("in serial_event_handler %x", event);
 break;
 default:
 break;
 }
} 
 
 void init_rs485();
void serial_event_handler(struct nrf_serial_s const * p_serial,
 nrf_serial_event_t event);
void send_rs485_message(char *buffer, size_t length);

// Setup UART0 for IPN
#define IPN_BAUDRATE 0x8A6000
#define UNUSED_PIN 0xFFFFFFFF
#define RS485_TX_PIN NRF_GPIO_PIN_MAP(0, 6)
#define RS485_RX_PIN NRF_GPIO_PIN_MAP(0, 5)

NRF_SERIAL_DRV_UART_CONFIG_DEF(m_uart1_drv_config,
 RS485_RX_PIN, RS485_TX_PIN,
 UNUSED_PIN, UNUSED_PIN,
 NRF_UART_HWFC_ENABLED, NRF_UART_PARITY_EXCLUDED,
 IPN_BAUDRATE,
 UART_DEFAULT_CONFIG_IRQ_PRIORITY);

#define SERIAL_FIFO_TX_SIZE 64
#define SERIAL_FIFO_RX_SIZE 64

NRF_SERIAL_QUEUES_DEF(serial1_queues, SERIAL_FIFO_TX_SIZE, SERIAL_FIFO_RX_SIZE);

#define SERIAL_BUFF_TX_SIZE 1
#define SERIAL_BUFF_RX_SIZE 1

NRF_SERIAL_BUFFERS_DEF(serial1_buffs, SERIAL_BUFF_TX_SIZE, SERIAL_BUFF_RX_SIZE);

NRF_SERIAL_CONFIG_DEF(serial1_config, NRF_SERIAL_MODE_DMA,
 &serial1_queues, &serial1_buffs, serial_event_handler, NULL);

NRF_SERIAL_UART_DEF(serial1_uart, 0); 
 
 I also read this question. 
 Is this the error mask?

Please help, 
 Thanks