Filed last week on behalf of a client and acknowledged as a bug yesterday. I posted this ARTICLE on my blog last week when I first documented it.
There are two types of structural framing family templates: (see attached image)
When you have both types of structural framing families loaded, place a family that uses the Complex and Trusses.rft. Then sketch a family based on the Beams and Braces.rft.
Then try to place a new truss instance. You should get this error message. (see second image)
The workaround I have settled on so far is to use a Generic Model category instead which is unfortunate.
Revit support advised that dragging a new truss instance from the Project Browser instead of using the Component command will allow the beam to be placed. The issue is with the Component command itself.