Strange error when adding a column

Question

I am trying to run the following SQL but get this error:
ALTER TABLE s1_grainsmart_option
    ADD ppv_flag                   char(1)       DEFAULT 'N'   not null
        CONSTRAINT ckc_gso_ppv_flag CHECK (ppv_flag IN ('Y','N'))
ERROR:  a problem occurred while running script 1700050069
  ORA-02293: cannot validate (GRAINV17UNICODE.CKC_GSO_PPV_FLAG) - check constraint violated
Here is the table definition:
CREATE TABLE s1_grainsmart_option
   go_key                          number                      not null,
   ps_same_number_flag             char(1)       DEFAULT 'N'   not null
       CONSTRAINT ckc_gso_ps_same_num_flag CHECK (ps_same_number_flag IN ('Y','N')),
   wheat_board_req_flag            char(1)       DEFAULT 'N'   not null
       CONSTRAINT ckc_gso_wb_req_flag CHECK (wheat_board_req_flag IN ('Y','N')),
   multiple_currencies_flag        char(1)       DEFAULT 'N'   not null
       CONSTRAINT ckc_gso_multi_currencies_flag CHECK (multiple_currencies_flag IN ('Y','N')),
   ar_software_interface           varchar2(30)                null,
   ap_software_interface           varchar2(30)                null,
   gl_software_interface           varchar2(30)                null,
   inv_software_interface          varchar2(30)                null,
   gl_by_location_flag             char(1)       DEFAULT 'Y'   not null
       CONSTRAINT ckc_gso_gl_by_location_flag CHECK (gl_by_location_flag IN ('Y','N')),
   CONSTRAINT pk_grainsmart_option PRIMARY KEY (go_key)
       using index
       tablespace smartsoft_index
tablespace smartsoft_data
BTW, there are several (approx. 200 "flag" columns) additionally; I didn't want to burden the "create table" definition.
I don't understand the error; I use this syntax for adding a mandatory column with a default value hundreds (if not more) times but in this case it issues an error.
Oracle 11.2.0.4 64-bit Standard Edition on Windows 2008 R2 Server.
Thanks
Murray

Answer 1

OK. Then it could be disable constraint, insert/update, enable constraint. In any case, we need exact output.
SQL> create table tbl(c1 number);
Table created.
SQL> alter table tbl ADD ppv_flag                   char(1)       DEFAULT 'N'   not null
  2          CONSTRAINT ckc_gso_ppv_flag CHECK (ppv_flag IN ('Y','N'));
Table altered.
SQL> alter table tbl disable constraint ckc_gso_ppv_flag;
Table altered.
SQL> insert into tbl values(9,'X');
1 row created.
SQL> alter table tbl enable constraint ckc_gso_ppv_flag;
alter table tbl enable constraint ckc_gso_ppv_flag
ERROR at line 1:
ORA-02293: cannot validate (SCOTT.CKC_GSO_PPV_FLAG) - check constraint violated
SQL>
SY.