Inphektion, the exception you saw was probably caused by pressing the Start button with a blank timer or alert field. This bug has been fixed in version 0.5 (just uploaded). Also, make sure your secondary alert times don't contain seconds (i.e., an alert time of 400 would be 4 hours, not 4 minutes). Anyway, install the new version and let me know if you still have any problems.
Version 0.5 also fixes a couple of other bugs (two little ones, and the "vibrate only" bug mention in a previous post). It also adds a couple of features, including an "elapsed time" mode, and an optional fast-and-high-pitched alert tune.