Certain hard disk formatting application programs can cause the Quadra DOS Compatible and DOS Compatibility Card drive container not be recognized. Two formatting applications that are known to cause this issue are SCSI Director, and APS Power Tools; a version of SCSI Director bundled with drives from Alliance Peripheral Systems. Other hard disk formatting applications may produce similar symptoms.
To correct the issue, you need to make sure that Finder Eject is disabled. Finder Eject should only be used for removable media. Consult the software's User's Guide for specific information on disabling Finder Eject.
Once you disable Finder Eject, you need to restart your computer and select the drive container in the PC Setup control panel. You can now switch to MS-DOS. You should restart the computer and switch to MS-DOS again to confirm that the issue is resolved.