SO2 detector (F&G) Calibration problem!

We have some SO2 detectors of Honeywell. The full range selection option in the instrument is only available for0-15ppm/0-50ppm only. But I don't have either7.5ppm/25ppm Cal. Gas. I have10 ppm Cal Gas only. When I am trying to perform Span Calibration of the Transmitter with10ppm gas (at a full range of15ppm/50ppm its showing "SPAN FAIL") But the instrument sensing SO2 gas well. But its showing a warning message "W-01" means "Calibration not performed" Sensor: CiTiceL®4S Rev.2 Sulfur Dioxide (SO2) Gas Sensor (Part Number:2112B2015) Transmitter is XCD RTD (Part Number: SPXCDALMTX4)