Is your number field a calculation? It seems not because you're trying to import into it. So it seems to be an auto-enter calc?
I think I'd set it up as an auto-enter calc with the calculation of 0. When you import your records, the 0 will be created but then over-written by the 1 that gets put in there. I'd make sure that the "Do not replace . . ." box under the auto-enter options is unchecked.