Hi
Don't know about you but when i have this problem 99 times in 100 its a field in the main table set to Required = true. Usually a text field, for some reseason when ever i create a table the text fields are always set to that. Anyway back to your problem. I would double check that;
a) You genuinley haven't got two different field types like memo not text or single not integer etc
b)Your main table fields allow nulls if there are any in your temp table.
c) That you haven't got a validation rule that's breached i.e >=0 and your trying to enter -1
d) Your not trying to enter a duplicate value into a field that's set to indexed = yes (no duplicates)
If that don't work i haven't got a Scooby.
Chris