This Data Definition error occurs when a key pairing is lost between the .med file and the .hsl file (or other supporting files required to make a method work). The best way to resolve this issue is to restore the method files from a backup, typically a package file that is exported during the programming process. Backing up regularly is highly suggested to avoid issues like these as well as be able to recover from problems that might occur in or outside of VENUS.
Thank you,
Dan