First of all, it sounds to me like you simply need the Motion Axis Move (MAM) instruction. This will allow a single axis to perform a point to point move, which is what it sounds like you are looking for.
The MCLM instruction will coordinate the motion of two or three orthoginal (X, Y, Z) axes to perform a linear motion in two or three dimensional space. This instruction only works if the axes are orthoginal. Many application don't need the motions coordinated. Many pick and place applications, for example, don't need the X and Y direction motions coordinated. Each can finish as soon as it can and things are OK. You don't care about the actual path the item takes as long as it ends up where it is supposed to.
However, consider a machine that needs to draw diagonal lines on a paper. To do this given the X and Y direction setup you need to run both x and y motors in a coordinated fashion since the path of the item through space is what defines the diagonal line. In this application you would use coordinated moves. You specify the desired Cartesian (X-Y) destination and the linear speed along the item path. the motion controller takes care of controlling both motors to follow this path.
Like I said, you probably want to look into the MAM instruction. That should take care of what you want to do.
Keith