User calls me: " I am sometimes getting an error message."
Me: "What did the error message say?"
User: "I don't remember."
Me: "Was there more than one type of error message?"
User: "I don't remember."
Me: "Well then what were the symptoms? How was the computer behaving different than normal / usual?"
User: "Nothing I know of other than the error messages ..."
Me: "Call me when the error message pops up again or, if it is inconvenient then, write down what it says and call me later."