Are there any Insert Triggers on the table? Have you tried running this from a SQL session outside the application?
Is bch_no defined as a not null column? Alternatively do you have not null columns in inv_01_07 which aren't listed in your insert statement?
insert into smlbhone.inv_01_07 (BAS_COD,ITM_COD,BCH_NO,EXP_DTE,ALC_FLG,BCH_STA,ITM_QO1,ITM_QO2,ITM_QO3,ITM_VAL,ITM_RAT,
Your insert statement is putting the value 300 into BAS_COD - so we know that that isn't null. However, your error message is referring to a table in the "BBB" schema and not the "SMLBHONE" one that you're showing in the insert statement.
Do you have another process/trigger that is supposed to be copying values from this table to another schema and this process is broken?