stability in the "UART" communication over BLE.

Hi I have a serious problem with stability in "UART" communication over BLE. I use the command: err_code = ble_nus_send_string(&m_nus, &bleBuffer, 20); where I send 20 bytes from bleBuffer. the err-code returned is 12292 = 0x3004. As I read it, the errors are: NRF_ERROR_SOFTDEVICE_NOT_ENABLED in NRF_ERROR_STK_BASE_NUM (0x3000) ///< STK error base

Can you enlighten me on the cause of this error, because the soft-device is enabled at the point.

Best regards and thanks in advance Benni Kleis Andreassen