Ora-20542

Environment : Oracle 9.2 on Windows
Using SQL PLus I issued next command:

ALTER TABLE MYTABLE ADD COL1 NUMBER(1) DEFAULT 0;

I got error messsage ORA-20542.
In documentation I was not able to find anything about this messsage.

After this I issued:

ALTER TABLE MYTABLE ADD COL1 NUMBER(1);
ALTER TABLE MYTABLE MODIFY COL1 DEFAULT 0;

And everyting was OK.

Any idea what is the reason for this.

Thanks