I have that jack, and had that exact problem, only in cold temperatures (25-40 degrees). I squirted some motor oil into the jack from the top, and although it ran out the bottom onto the ground, it freed the jack up nicely.
This technique may not be recommended, but it fixed the problem for me!
"Money frees you from doing things you dislike. Since I dislike doing nearly everything, money is handy." Groucho Marx