HeLen ,

I changed everything that you described , but still receive an error.

It's not inserting/editing ID_Lookup field directly, but choosing it
from DBLookupComboBox ( on main form is very BOLD - ERROR ) .

I'm posting a new test file big_int_test2.rar with all the changes
and with compiled app on D7.

Try to compile it on D6 and choose ID_Lookup from ComboBox on right
side. Maybe it's something with D7 ?

Goran