First, try it with the IK off for both feet.

If that doesn't help try using walk designer in the same poser document rather than adding it as a pose.

If that doesn't work, does it just jump once? If so move your figure to the start point on frame one. Then with the figure selected (the whole figure, not just a part) open the graph editor and select the X trans and drag the slider so you can see the entire animation. There should be a hash mark on every frame with the first one being obviously in a different place. Click on frame 2 and hold down the shift key and select all the little hash marks to the end. Then with the cntrl key (perhaps command on Mac, but not sure) drag the line so the second hash mark lines up with the first. Do the same for the z trans (and y if you have your figure at a different height). This only works if your figure is facing the same direction. Trying to rotate a figure once you've applied the walk doesn't usually work, at least not for me, since walk designer moves the whole body and not just the hips.

Last resort, save the the top half of the animated pose by clicking on "select subset" after you hit the "+" button to add it to the pose. Then select only the parts you want to be animated. Do the same for the walk as well. Doing it this way will let you combine them. If your figure is turning to wave at someone while walking, save only the arm that is waving and the abdomen, the chest, the neck and the head to your pose folder. Then open the walk file and save only the hips, legs, feet and perhaps the arm that isn't waving otherwise it won't move. Then you can apply the two separate poses and they won't overwrite one another.

Hope that helps and isn't too confusing!

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