When you assemble the knife you want to make sure the liners and blade will remain centered. If you assembled the knife with the blade in the closed position or half open and tightened the small screws in the wrong order you can get it misaligned.
This is how you want to reassemble:
Place the blade into the knife in the open position(lockbar locked). Then put the grips on and then slightly tighten the small Phillips screws from the rear end of the knife and then the ones towards the front. Then tighten the pivot screw and then back off (loosen) 1 1/2 turns. (all this while the blade is in the open and locked postion!!) then tighten the small Phillips screws all the way down..(again from the rear of the grip towards the front-first the two rears and then the middle ones) now tighten the pivot screw 1 1/2 turns to its desired position. Then close the blade and see if the blade is centered. You can then adjust the pivot swhile the blade is closed to perfect it to make sure the blade is centered. The blade may move when doing this.
When dissembling the knife the liners and grips can shift causing the blade to lean or the lock bar interface not to touch the tang properly.
You should not have any problem then.