This can happen sometimes especially if the pole is not taken down correctly, it is a safety mechanism. The most common reason locking nuts get stuck is because people make the mistake of turning the black adjuster bar BEFORE first loosening the locking nut. This can get the pole stuck. Other factors that can cause it to get stuck are environmental like humidity. Temperature flucuations cause metals to expand and contract which can cause metal parts to stick together.
To fix the problem: It is very important that you FIRST loosen the silver nut on the black adjuster bar by turning it Counter-Clockwise until it is about an inch or two above the main pole A. Then you can turn the black adjuster bar Clock-Wise to loosen the pole from the ceiling and lower the dome.
If you accidentally try to turn the black adjuster bar before properly loosening the silver locking nut, it will tighten the pole in place. Once that happens it can be a challenge getting it un-done but not impossible. I personally like to use a good pair of soft grip channel locks or a pipe wrench to get the locking nut to turn much easier when if it's too tight or stuck. You can also spray the threads of the black adjuster bar and locking nut with WD-40, this will make it easier to loosen the locking nut. IF you do use WD-40, clean your dance pole REALLY well immediately afterwards to ensure no WD-40 residue is left on the chrome finish. It's a very slippery, lubricated substance and can cause you to loose grip on the dance pole if it is not thouroughly cleaned on the dance pole finish.