What causes the error "Bad XEF or ZEF file format" when importing a Concept .ASC file into Control Expert (formerly Unity Pro)?

Issue
Concept .ASC file can not be imported into Unity Pro.

Product line
Unity Pro, Concept, Control Expert

Resolution
This error can occur when the Concept project was not exported out of the Concept Converter using the first option, "Project with used DFBs".
If "Project with used DFBs (Re-Connect to Equal)" is used the file will not import.