Yep, what he said. And in your case too, unfortunately you might have run afoul of the dreaded bent plate syndrome.
If this has been a hard door to open and close for awhile, one of the actuating plates/levers within the latch mechanism might have become slightly bent and be jamming up where the lever from the door button rod is trying to push it. Instead jamming up on it.
So if the cleaning does not do the trick, you might have to pull it out and slightly re-bend the offending lever.
With luck though, a good cleaning will take care if it.
Have fun!
Paul