Welcome to the forum.
I use the ResMed AirSense 10 machine and have only seen the red sad face once. That was when I was trying a new mask and I did not have it adjusted tight enough to seal. The leaks were really quite bad.
As a first thought is there any chance that your mask type is not selected properly in your machine? There should be three settings; Full Face, Nasal, and Nasal Pillow. The machine uses this to compensate for the intentional mask leakage. A large mask will have a larger purge leakage than a small one.
If you are using a nasal, or nasal pillow mask, is there any chance you are opening your mouth in your sleep?
Is your machine set up to display the more detailed sleep report? And, if so what leakage rate is displayed when you go to the detailed sleep report? If you don't have that option enabled but want it, just post again and I can tell you how to display it.
And, last it may be something defective with the machine. I am not sure if ResMed will answer calls directly, or if you have to go through your supplier. Unfortunately, I believe the warranty is 3 years...
If that is the only problem with the machine, there may be other ways to get around it, if it is only a happy face/sad face issue. I generally do not use the machine to get my data, and instead use a free software program called SleepyHead to display the detailed sleep data. If you have any interest in that, just post. It does need a PC, or Mac, and an SD card reader. It may also help you diagnose the mask leakage issue.
Hope that helps some,