Record is deleted. That's the error message when I tried to edit the #Deleted memo field of particular records.
Consequently, I cannot change this corrupted memo field.
Solution: Tools -> Database Utilities -> Compact and Repair Database...
Now the Memo field is empty and free for modification.
This way I don't have to deleted and re-enter the whole record.
Source of Reference: http://www.bigresource.com/MS_ACCESS-Record-is-deleted-message--D6xmPD89.html#