Error message in ABAP objects for: 
 
FIELD-SYMBOLS <fs> STRUCTURE struc DEFAULT f.
Correct syntax: 
 
FIELD-SYMBOLS <fs> TYPE|LIKE struc. 
 
ASSIGN f TO <fs> CASTING.
Reason: 
 
Field symbols defined with the STRUCTURE
addition are a mixture of field symbols whose type is defined and a tool for casting on data types defined
in the ABAP Dictionary or locally in the program. The types of field symbols are defined with the 
TYPE addition of the FIELD-SYMBOLS
statement and the CASTING addition of the ASSIGN statement can be used for the casting.
Overview: 
 
Replacement for Obsolete Statements ABAP Objects