copy location z-axis

i’ve got a little problem. Everytime i use the copy location constraint with offset the object that is copying the other one seems to have moved its z-axis. I’d just like to know why this happens.

I’m not sure exactly what you mean, but I guess your objects have different local coordinates (i.e. the Z axis of the second object is pointing in another direction than the first). You can use the Transform Orientation pop-up menu (under the 3D view saying ‘Global’ by default) to see if the local coordinates of one object are the same as the global coordinates.
Alternatively, before applying your constraint, select your second object and press Alt+R to clear the objects rotation.

Hope it helped
/ Mats