Can’t make an smart PDF using the project publisher

When running the project publisher I get following error, what does this error mean and how do I solve it? this prevents me from making a smart PDF from my drawings.

When I select “individual PDF’s” in the project publisher, then I receive only the PDF’s from pages were the source page is an DGN file. Its appears that most of my pages are DWG, can they be converted back to DGN.?

My project is an old backup from promise that is at least 8 years old.