I need an elementary Library Tutorial ... I have watched many videos (good videos), but I am missing something fundamental. Not sure there's an easy way to explain or solve this - but, here goes. I want to build a library of C-Channel profiles that I may extrude to specific project lengths to populate my Bill of Materials.

So, I have tried creating a sketch or copying an existing sketch of C-Channel, dimensioning until fully defined, and saving the sketch to a "Test" Library using the "Add to Library" Icon from the Design Library Task Pane. Doing so gets me the menu for adding the sketch and I do assure I am selecting to add it as a LibFeature NOT a Part in the pull down menu. Everything in the saving process looks correct. I get the little "L" next to the feature in the feature tree and I see the new Library item show up in the Library Folder. HOWEVER, when I try to drag the item into a new part I get the error as seen below. What's up with that?

(Tried pasting a screen shot, but it won't display - please see attached file for SolidWorks Warning)