I have an object that I'm trying to combine the parts back together. These two pieces were once together a long time ago and have not been altered in any way. I combine and merge vertices to one side and it all works out fine. I do the same to the other side and the thick border edge line remains thick after combining and merging. Both sides of the thing I'm modeling are exactly the same yet the left side merges back fine with no thick border line, and the right side matches up and connects fine but the thick border edge doesn't go away. I've checked for extra vertices that could be causing the problem I've tried just about everything I could and I still end up with this problem.
I tried explaining it the best I could without pictures. If you need to see what I'm talking about let me know and I will take a couple screen shots.