SQL & PL/SQL

I tried to drop a column from a table, alter table table1 drop column col1234;

But it return error,

ORA-00604: error occurred at recursive SQL Level 1
ORA-00001: unique constraint (SYS.I_COL_USAGE$) violated

Any idea what is going on??

I already drop all the indexes, constraints in this table (except primary key), but the column still can't be dropped!