I am actually going through the Planar Mechanical User's Guide and following the instructions step by step. I added the "Planar Mechanical 3D Viewer" and the "Planar Mechanical Assembly" icon. In the guide I am told to first open the 3D viewer and later the assembly but when I try to open the assembly I get the following error message:
"An planar assistant icon is already on the sketch
Use only one planar assistant by circuit"
After that I cannot open either of the assistants.