This message is displayed when the scale Analogue to Digital (A to D) converter doesn't see enough change from zero to the calibration weight value.  Normally this is a problem when using only 40 kg for calibration.

Things to try:

1. Try using 100 kg for calibration (increase the calibration weight).
2. Check that the load cell cable from the indicator to the scale base junction box is connected and in good condition. If it's damaged then one could be able to get a zero calibration but not see the change in weight when span calibration is being done, and therefore the indicator will advise that the weight is too small.
3. Go into the scale diagnostic screen and check that the A to D reading increases with the addition of weight applied to the scale.