When using a heat storage model, I get the error message ‘Index out of bounds’. What does this mean?

Heat storage tanks are defined in Green City as layers of superimposed media (usually water). The number of layers is set via the parameter ‘n’. Each connection (1 to 6) is assigned a layer index as the inlet or outlet height. This is also done via separate indices (iFlow or iReturn). If these indices exceed the number of layers ‘n’, the above-mentioned error message is displayed.