Is there an option in Options/Preferences to turn the log on/off or set its size? You may want to try copying and pasting the existing log into another document (WordPad/NotePad will work well) and then delete the existing log. You could also rename the existing file and then let it start over. I haven't used WinFax but I encountered a similar problem in other programs when the log file filled up.
To ME or NOT to ME....