Okay, I know this is still controversial, but I can tell you Mocha threw up not long after I gave her some Greenies. My shihtzu did the same. I never give them any more greenies after that.
Also, I feed Mocha at 6/7am, snack at 1/2pm, then feed again at 5/6pm, she hasn't had any problems.
I think people can give better answer if they know what you are feeding him
a lot of times it's the main meal that causes so much problems.