I think you may not be placing the track link associated with the load/unload asset if I understand your post correctly. Here are some screenshots of what to keep a lookout for;
Pick the crane from the list with a left click, now without clicking place the crane where you want it - you can rotate and make adjustments to its position after you do the next step. Left click once more and you should see a yellow line on the ground in the center. Move the mouse around if you don't see it at first and don't mouse click till you do the next step.
One.jpg
Now move the mouse, again without clicking, over the track and you should see a white box with orange ended arrows appear on the track. As soon as you have that track link then left click again to set it in place. At this point a 2nd crane immediately appears at your mouse position and you can go ahead and right click this time to dismiss it.
Two.jpg
Now, finish up your placement by rotating the crane and moving it so the blue frame is lined up and centered on the track. You can also grab the track link and slide it up or down the track and place it so its centered in the blue frame - the blue frame does not appear in the game, only in the editor to show you where the containers will be lowered onto waiting baretables.
three.jpg
I hope this helps. Most things that are track linked work pretty much the same way - left click to select - left click to place - left click when the track link is in the right position to set it.
You do not have the required permissions to view the files attached to this post.
Download the PRB from page 51 of the Powder River Basin thread.