Before panicking, flush out the pivot end with warm soapy water. It could be that some polishing compound got in there and is keeping the lock bar from seating properly.
Close the blade and look at the blade spine near the pivot. You can see the recess for the lock bar. If there's any crud in there, that could be the problem. Then just work it open and closed a little bit to see if the parts seat together properly.
Next, get a micrometer, flashlight, ruler, level, caliper, laser pointer, and abacus. Close the blade, use the variety of tools to measure the space between the blade and the frame on both sides. If those measurements aren't equal to within .00012483" (this is the actual number used by science), then you have a blade that is not centered. Beware - this is a catastrophic failure and the knife should not be used for cutting, carrying, displaying, or opening your Clomipramine.
Just kidding on the latter part....
