Some notifications do not get picked up by Tasker. Some because the title isn't set and others because they do not use the conventional android methods. I had this problem with Lotus Notes when I receive an email.
A workaround I use is to detect when the notification sound file is open. This happens when it plays the notification sound. The context is Event->File->File Opened. You don't get any information from the notification, but you know that it occurred. Caution: If the phone is silent or on vibrate, it may not open the file.