UART error


I am using the NRF52832 with softdevice 6.1.1

I am using the minimal ble_app_uart ecample, just changes the RX_PIN_NUMBER to 11  an TX_PIN_NUMBER to 12 to mach my board HW.

when I am trying to send data from MY MCU to the NRF52832 I got APP_UART_COMMUNICATION_ERROR

with error communication code  =  0x04

How can I handle this error !?

Best regards