I have create a walk for a cat that is 150 frames long. I had originally wanted to bring it as is, into my NLE program and move the cat using the tools in the NLE, but this proved to be taxing and painstaking to get it right, so I decided to put the cat on a straight path, so I would get an even walk of the cat on a straight line (looking at it in Profile) from point A to point B, except when I try it, the cat doesn't walk the line and still walks in place - is there something that I am missing?

To have a figure follow a walk path in Poser, you must use the Walk Designer.

Window menu --> Walk Designer (or SHIFT-CTRL-S)

Unfortunately, the Walk Designer is designed for bipeds, so for animal figures like the P4 cat or MilCat, you'll also need an animated walk pose, 30 frames in length, that loops well. Place it in your /Runtime/Poses/Walk Designer folder; it'll show up as a blend style in the Walk Designer.

HaiGan has a Walk Designer-compatible pose for the P4 cat here in Free Stuff. Follow the instructions in the zip file carefully. The Walk Designer can be glitchy at times, so patience and a willingness to "try, try again" is highly recommended.

I have that add-on already, the walk looks good, but how do I attach it to a path?

Figure > create walk path. By default Walk Designer uses the walk path. If the cat is following the path, but it's feet skid, well that's as good as it gets. WD isn't really for quadrupeds.

It is not following the path at all.

What version of Poser?