If an error occurs, the Gateway Error Logs should be checked first. There two transaction to check the Gateway related errors:
To reach the Frontend Errors, use transaction code /IWFND/ERROR_LOG or you can reach it from transaction /IWFND/GW_CLIENT by using the dedicated Error Log button.
To reach the Backend Errors, use transaction code /IWBEP/ERROR_LOG in the backend system or you can reach it from transaction /IWFND/ERROR_LOG by using the dedicated Backend Monitor button. It will redirect you to the backend system.
The checkbox in the "Backend Error" column indicates that wether errors occur in the backend or not.