Error codes exist in the model to warn the user of inconsistencies and errors. The model is released to the community as a package which should not trigger such inconsistencies or errors. However, the user may change the code or modify the input files in a way which triggers such a message. The user may even simply operate the model on a platform which brings up an error message. In many cases these errors will cause the model to terminate in order to alert the user of a problem which will render the simulation useless or will cause it to fail later.
In general, when an error message appears, the user must switch gears from production to debugging mode. The error message may make the corrective measures obvious. If not, the user will need to find the line in the code which wrote the error message and gradually back track until the cause for the error is found. The old fashioned placement of write statements in the code or, if available, debugging software may help understand the problem. When using debugging software, it is useful to change DEBUG to TRUE in the jobscript.