Using the Display events in > Text file > Active and Display events in > XML file > Active options of the Event View panel you can tell the Event View engine to output the events to a .txt and/or .xml file. AQTime displays this message when the Active option is enabled, but the name of the text (or xml) file is not specified.
To solve the problem, open the Event View Panel Options dialog and specify the text (or xml) file name.