Can you capture screen images of the tree with everything you have set up in the simulation?
Have you applied any fixtures to it yet?
If you want to send me the file I will try playing with it and see if I can't get the load applied. I am guessing it is something minor.
My email is dustin at cornhusker800.com
Attached is a picture of my Feature Tree.
As you can see I have a couple of fixtures. My assembly has a ring on the bottom that rides on these shafts. I was not sure about the best way to represent this in SolidWorks, so I create circular split line surfaces on the bottom of the ring and fixed them. I then added a cylindrical fixture to present a bearing about which the frame rotates.
I have it figured out for you. You had the parts of your study being treated as beams, when solidworks does beams in simulation it only creates a simple line to represent the part. If you select those peices and right click there will be an option "treat as solid". That will allow you to pick a face or bolt hole to apply a load to.
This response is specific to the image in your original post. You should select the option "selected direction" and it will make visible options for applying loads to beams. You need to select this as a beam element is a line element and as such has no geometric cross section (it is represented by numbers in the beam element). Thus you need to specify a direction for any load applied to a beam. You can apply loads to the end nodes (where it connects to other beams or is free) or along the length directly. If you want an arbitrarily located concentrated load you need to put a reference point on the beam (under the reference geometry menu in SWX).