Error referencing AutoCAD files...

I am running FDOT SS4 MR11 and I am getting an error when I try to reference a .dwg file sent to me by a sub-consultant. The error says that the file type is not supported. I am also running the most recent version of RealDWG. My early research tells me that the issue may be due to the newest version of AutoCAD not being compatible. Is there something I am missing? This type of error did not seem to be an issue until recently, so it could also be the newest release of SS4?

Any knowledge or advice is appreciated!