Here are the steps you should take:
1) Do a file-by-file backup of your volume. Keep in mind that a
file-by-file backup will not retain access privileges, so you'll have
to recreate them if you need to restore from this backup.
2) Since the volume is not available to the application, you will
have to re-prepare the volume for use with AppleShare and recreate the
parallel directory structure (PDS). You will lose access privileges
doing this -- but you'll lose no data. This should get you back to a
functioning server.
3) If the problem persists, reinitialize your volume, prepare for
use with AppleShare, and restore all your files from the backup you did
before starting.