10 year old gelding

Question
Acquired this horse in Mexico where I live. He was a beach rental and ranch horse.   
Men ride him and he goes fine, a female gets on him he won't move.I have tried turning him in circles, most of the time I try turning him I can pull his nose to my stirrup he won't move his legs.
Spurs,crop, whip, he won;t move. Someone can lead me riding him he will move but, will try to stop.
He is in great condition, no pain and in great health.
I am going to put him the round pen, then get on him in the round pen.
Hope you can send me some other suggestions.
I have had my own horses for 60 years just want a willing horse for causal ridding.

Answer
    Hi Jan,
  I would like to apologise for the delay in responding. This was due to the time of year, plus the fact that we have had record breaking severe weather, which caused many problems.
  Your problem sounds very strange, and is certainly something I have not come across before. I am afraid that I don't have a cure for you. The only suggestion I can think of is something to startle him. You could try taping or tying a smallish plastic bag to the end of a piece of stick. Try it first in the round pen unmounted. Fit him with a headcollar and attach a longish rope (to allow him the freedom to move). Have someone hold him stationary. The person with the new weapon should keep it hidden from him and ensure that it does not rustle before the time is right. This person should go behind him, and producing the stick, shake it vigoursly. He could ignore the whole thing, in which case you are going to have to try to find something else to startle him. He could overreact and shoot forward or he could just walk on. Either way it is imperative that the person with the stick stops shaking it immediately. The sound of the plastic rustling is intended to be a cue for him to move and if he does, the sound has to disappear. Try to experiment to find the right distance for the person behind to stand in order to get him to move without causing him to panic. You could practice this quite a bit to clearly imprint on his mind that he has the power to get rid of the annoying sound by simply moving his feet.
  If all goes well, you could try it mounted. In this case timing is of the essence. As you give him a nudge with your leg say the word "now" out loud, and the person behind starts shaking the stick.Once again, if he moves, the person with the stick has to stop shaking it immediately. The idea here is to make use of his power of anticipation. Before very long he will start to expect the rustling sound to start right after he feels your leg, and will hopefully move from that cue alone.
  I would like you to get back to me, before you try any of this, to let me know if you think it might work, and if you would be happy to give it a shot.
         Slan,
                  Brendan