Transition with walk cycle I made a walk cycle action : the character has nothing in his hands.
Then, I made an action to take an object.
Then, I would like my character to keep his path, using walk cycle action again, and with the object in his hands.

The problem is that the walk cycle action does not work when there is the object in the hands.
More precisely, I think it is because I made a mistake while doing the transition between the action to take the object, and the action to start again the walk cycle action.

How do you do such thing properly?
We have to guess, as you did not provide us with a minimal example file that demonstrates your issue. Most likely, the "object in hands" action contains fcurves for the rest of the body too, not just the arm/hand holding the object. These then override the walk cycle. If my guess is correct, the solution lies in removing the lower body fcurves from the "object in hands" action.