Error queue
Each error state in the instrument leads to an entry in the error queue. The entries of the error queue are detailed plain text error messages that you can look up in the error log or query via remote control using SYSTem:ERRor[:NEXT]? or SYSTem:ERRor:ALL?.
Each call of SYST:ERR? returns the newest error and clears it from the error queue. If no error messages are stored there anymore, the instrument responds with 0, "No error".