See the section Filename Mapping in the chapter Advanced Operation and the section Database Reference File Maintenance in the chapter Database Integrity for more information on the /fs option.
Resolution:
If the option has been specified on the command line, include the /af option to specify the name of the replacement string value and retry the operation.
If the option is specified in a database reference file, this error indicates that the database reference file has become corrupt or has been changed without using the Database Reference File Maintenance Utility.
In this situation, it may be possible to remove the invalid entry using a normal text editor. If this is unsuccessful, discard the current database reference file and create a new one using the Database Reference File Maintenance Utility.