Error messages are only implemented for input data. At present there is a fairly loose range check on each value input. If the input value is out of range the standard Microsoft warning message is presented and the value remains at the present value.
Normal termination provides a message that asks if the data as it is should be saved. This will happen only if the "yes" button is checked. In any event, on start up the same default case will appear. In order to work on or modify an old data set it is necessary to load it with the File|Read command.