drop public database link problem(very urgent)

  hi
we have a db link which has been created long ago and it is public databaselink


OWNER                          DB_LINK                                                 USERNAME                       HOST        
------------------------------ ------------------------------------------------------- ------------------------------ ------------ ------------------

PUBLIC                      db1                                                      user01                                          db1   
when i want to drop it i encounter below error


SQL> drop database link  db1  ;
drop database link db1 
                   *
ERROR at line 1:
ORA-02024: database link not found


SQL>  drop public database link  db1  ;
 drop public database link db1 
                           *
ERROR at line 1:
ORA-02024: database link not found

no mater with what user i try i still get this error.
Please kindly assist.
i also tried changing global db name it did not help