There are essentially two different kinds of error message. One is caused by the user making a mistake in what he or she types in - a syntax error, a spelling mistake or giving the wrong name or pathname for a file. The other kind is when the computer runs out of memory or runs into mathematical problems like trying to divide by zero. Things are not quite so clear-cut, because in fact the commonest reason for the program to produce the second kind of error message is also because the user and told it to do something silly, like make a chi-squared table with zero rows. We have tried to trap most of these errors, but a few have got through.
If you get an error message, first check carefully that you have not made a typing mistake. If not, and especially if you get one of the "out of memory" messages, then it may be that you are exceeding the program's capacity. Although we have tried to guard against it, there is a risk that the program may crash or "hang up", which means that absolutely nothing at all happens when you push any of the keys. Because of the risk of this, if you get an error message which you cannot otherwise explain we advise you immediately to save your data to a file and to close your output and log files. Do not save your data to the same file that you read it from, but to a new file with a different name. All these precautions are to minimise the risk of an error in your program damaging ("corrupting") any of your files or leaving you stuck unable to save your data.