The sticky black tar is creosote & needs to be removed from the ceiling of the smoker at least.
You can leave it on the sides & bottom without any problems, but when it melts on your food it's going to make it bitter.
It is caused by producing thick white smoke in your smoker. What are you using to produce the smoke?
Most of the MES guys use an
AMAZEN tray & burn pellets or dust in it for the smoke.
http://www.amazenproducts.com/
If your using the MB cold smoker attachment it needs to be separated from the smoker with a length of pipe so the creosote will stay in the pipe & nice clean smoke will get into the smoker.
If your using the factory chip loader don't overfill it. Just keep adding small amounts every 30-40 minutes.
And last, MAKE SURE THE TOP VENT IS 100% OPEN.
You want to see nice light blue smoke coming out of the vent, not thick white smoke.
There are a thousand ways to smoke ribs & everyone thinks differently on this subject.
But here is how I do them, maybe this will help you.
http://www.smokingmeatforums.com/t/240916/perfect-ribs-every-time-this-really-works
Al