There are a couple of things to check.

1. Make sure the foot is not locked in the Motion Layer panel. If it is, just click the little padlock beside it.

2. Make sure you don’t have two key frames right next to each other on the timeline. Zoom into the timeline, and chose the one you want to keep and delete the other. Almost every time I have had that issue, that fixed the problem for me. It drives me crazy when iClone does that, because I tend to work against deadlines, and this is just one more thing I have to do.

Good luck!

Thanks for your response, but this is not the case. No foot locked and no close key frames.
I am actually working on a rabbit climbing a ladder.  I start fixing the first position (let's call it A), then I fix the second position (let's call it B), and then I check the movement in between.
Suppose I find something to adjust in the middle, so I fix it, but at this point the B position changed, and I don't understand why, and I enter in a infinite loop of adjustments. 

I would suggest a quick study of the twelve principles of animation (YouTube it).  The EDIT MOTION LAYER can be really great, but also a gigantic pain in the ass.

You should probably start by blocking in all your CONTACT FRAMES for the entire sequence -- i.e. each point where the Rabbit contacts the ladder.  Run the timeline and move those CONTACT FRAMES until you get the timing correct.  Then go back to the start and do a PASSING FRAME between each CONTACT FRAME.  Study some basic walk cycle tutorials and you'll get the picture.  Then go back and do your IN-BETWEEN FRAMES -- i.e. frames between the CONTACT and PASSING FRAMES.

When you create your frames, pay attention to what it locked and what is not -- some parts (like the feet) are automatically locked).  Before you make adjustments, check which parts are locked.  Bear in mind that Inverse Kinematics can have unexpected effects when animating.  If I'm doing something requiring precision, I lock everything that doesn't need to move.

Another option is to place dummy objects for each "hand-hold" (i.e. contact point), and attach the Rabbit to them.  This should lock the contact point in place.

One last thing:  I am using Iclone 7.2 and there are two EXTREMELY ANNOYING PHENOMENA that are just part of the system: 1 -- sometimes the frame I animate is displaced by one frame to the left.  If you see this happening, move your cursor one frame to the offending location and animate from there,  Then drag those frames back to where you wanted them.  2 -- HIDDEN KEY FRAMES.  A key can sometimes be hiding under another key on the same pint in the time-line.  I know this should not be possible, but the only solution is to highlight the offending key and delete it.  If you do this, and it still appears to be there, then you will have a "hidden keyframe".  This seems to be caused by dragging another key over the top and Iclone not replacing the key underneath.

Good luck!

--Bex.

Thanks for yourinteresting answer, I agree with everything you say, it is the problem I amfacing. I'll follow your advice and search youtube for the twelve principalesof animation. But I ask you one more thing: when you say “If I'm doingsomething requiring precision, I lock everything that doesn't need to move.”perhaps this is the point that I need to understand better and learn more. 
I mean Isthere a way to define a CONTACT FRAME as being a frame where nothing can bechanged, completely and totally locked?
And all IN-BETWEEN frames are they alwaysand dynamically calculated depending on the CONTACT FRAMES?
What bothers me isthat a CONTACT FRAMES change by themselfs,although I think I have blocked everything, but it doesn't seem to be.
Atthis point the best way for me is to start all over again.

I believethat my way of thinking needs more learning.

Did you solve your problem?

If not, I may have the solution:  The Reach Effector tool.

https://www.youtube.com/watch?v=nBpykqhMDp0

By coincidence I ended up doing a ladder climb animation, and I remembered the tutorial above.  I made a contact pose of the character on the ladder -- both hands and both feet contacting alternate rungs, as if climbing (or in my case descending).  Then I mirrored the pose, giving me the contacts for a complete cycle i.e. left and right side).  Then I copied and pasted the alternate poses on the time line; then positioned each contact pose on the ladder by unlocking all the limbs in the motion editor, and positioning the pelvis (a bit like using FK).  Once I had a series of poses and they were all on the correct ladder rungs, I used the REACH EFFECTOR to alternate locking and unlocking the different limbs as they move from one rung to another.  After you have done this, you can go back into the motion editor and add secondary motion.

I'm sure this is probably really obvious, and second nature to someone who uses Iclone on a daily basis, but my schedule only allows me a couple of house a week to try things.

I hope this helps!

--Bex.

ok

very interesting. I will start from here to improve my skill :)