Probably rust in the drive opening. When I went to lower mine, it seemed like the extension was just spinning in the opening. I thought the square drive opening was rounded out. Once I removed the assembly, I noticed that the drive opening was just filled with junk, and the extension wouldn't insert far enough to be effective. Although I cleaned mine up, and got it to work, I replaced it with a new one. Also, if you get a long extension, instead of the supplied tool, you might have better luck. Keep working at it to get the opening cleared out. Good luck. As you can see by previous posts, these things usually need to be replaced.