Unfortunately, this spells disaster and is usually caused by a
   corrupted DBV file.  However, the FlexFile scheme is based on
   a very solid principal.  That is, if your DBF file holding the
   pointer-fields into the DBV file is intact, the V_RETRIEVE()
   function will almost invariably still retrieve data from any
   field that has not yet been corrupted.

   So, disaster recovery is as simple as creating a new DBV file
   in a new FlexFile work area and V_REPLACE()ing data into the
   new area with the data V_RETRIEVE()d from the corrupted area.

   Remember to test for V_TYPE() on the pointer-field because if
   it encounters a corrupted portion of the file, it will return
   an "U"ndefined regardless of the data type stored in that
   particular field.