Yes! I forgot about that. That is likely to be the problem. It is due to old lubricant which has thickened. As Chris says, move the lens rapidly clockwise/counterclockwise and it should complete the cycle. If not, warm it up. A sunny window might be enough, or putting it in an oven which is not above 120 actual degrees F, or a hair dryer blowing on the lens (being careful not to overheat any spot). Jiggle it periodically until you get it to release.
Once the lens is off, it is not difficult to get into the lens through the back to clean and relube it.
In this thread over on P.nut I explain how to do it: