I'm not sure what you have tried already, but I would try washing out the action thoroughly with hot soapy water. Press down on the lock spring release to lift up the rocker bar near the pivot area, and wash out the gap as you rotate the blade back and forth. The idea is to free up whatever grit is stuck in there. Then dry off the knife completely and blast the action with some of that canned compressed air available where electronics are sold (K-Mart has it). This should solve the problem, provided that the metal surfaces are not actually damaged.
By the way, WD-40 is good for cleaning out the action and eliminating water from metal surfaces, but it's not a very good lubricant. It can cause a gritty feeling similar to what you seem to be describing. I use either Rem-Oil or Dri-Lube (both produced by Remington). Lots of other products work well too.
Your Calypso should operate very smoothly. Mine does. Great knife.
I hope this helps.
David Rock