not to sound like a wise guy, but see if you are not holding your fingers on the lockbar while trying to open it
better than that, as Gianni from Lionsteel suggested, try opening it with your other hand, and that way the lock bar will be free from any additional pressure, and then you'll know if you're holding it right for an easy opening, or that you have a problem
if is still hard to open it with your other hand too, than you may have to send it in , or if you want to fix it yourself, maybe sand the edges of the hole in the blade for the ceramic ball, (edit) : though i wouldn't really recommend that