Did you have enough of the Stubbs lit? Sometimes it take a few extra minutes to really get the charcoal going. I use Stubbs exclusively and have never had that problem.
Give us a little more info on your set up. Are you using a charcoal basket? What kind of offset? How high up is your charcoal grate? Are you sure it didn't get choked off from ash?
Answer those questions and we should be better off with giving some help.
18.5" OTS, 22.5" OTG, CB Silver(Rip), Vintage Coleman Bullet, Pit Barrel, UDS