Which SSS trigger do you have? I had a similiar problem, but I had to remove/trim the stock a little more around the trigger area. Make sure all areas of the trigger are clear. All it takes is a slight bind to cause a problem like your having.

I don't think modifying the trigger guard is the answer. It could be causing the problem by putting a bind on the stock affecting the trigger. Again, I had one that had a similiar issue, loosen the action screw, no problem, tighten it up, the problem showed up. I knew something was binding the trigger and I eventually got it out by trimming the stock around all areas of the trigger. I did see a spot on mine where it was hitting the stock and I started there!

Of course, check the trigger guard very closely and make sure the trigger is not hitting it or close to it after tightening.