The FORTRAN routines return warning and error codes and messages when the input conditions are out of range or the calculations fail. The error codes are integers returned in the subroutine argument ierr. When a calculation is successful, the value of ierr is 0. Negative values of ierr signify a warning-that is, a condition where calculations were completed, but the results may be suspect. The most common warnings concern temperatures or pressures above the limits of the property model.

Errors imply conditions for which the calculations failed (such as an iteration not converging) or for which calculations are not possible. Many property models give completely wrong results when extrapolated to lower temperatures and/or higher densities, thus, errors are also issued when the temperature is below the limit of the model or the density is above the limit. The codes for errors are positive numbers.

In the interface, errors are displayed in an Alert box. If the calculation of a table results in a warning, a message is displayed at the completion of the calculations, and the individual messages can be displayed by clicking the mouse on the number of the affected row.