Missing Reference From File - Model Not Found

I am working in ORD - SS4 and designing an intersection of two corridors. I set null-point triggers in my template to control the display of certain components and created a template drop for the mainline corridor. For the secondary corridor, with it's template drop ending prior to the intersection, I created horizontal geometry that I intended to profile and use for creating a design surface.

After creating the horizontal geometry, but before creating active profiles for each element, I edited the mainline template drop to adjust which components will not display. As soon as I accepted these changes to the template (had not yet created my parametric constraint in the corridor bucket list) some of the horizontal geometry elements turned bold red with a small "x" icon. My Message Center displays the red "x" symbol with the message: "Missing Reference From File - Model Not Found".

I cannot select these elements for commands (such as create complex by element or create profile intersection point) while they are in this state. What did I do wrong? How can I fix this?