Is this a question or a statement? :)
If its a "this is my problem, can someone please help fix it" - then the error message is giving you all the information you need.
When adding a record, any required data must be set. You cannot have a null ID column, since, well, how do you ID something if its ID isn't set? It does not make sense!
Ensure you are setting the ID value for the record when inserting. You can do this a number of ways, use a GUID, increment based on the last used ID, create an ID based on the culmanation of various values etc..
What to use for an ID is always a hot topic of debate so I won't go there! :D