Ok I have found what is the problem. I will paste some comments about that error and you decide where to go and fix it. First of all it is the MSSQL error.
SET IDENTITY_INSERT [ database. [ owner. ] ] { table } ON
Don't forget to turn it back off again after!
SQL Server will automatically update its generated IDs to ensure you don't get duplicates after the insert;
the ASP pages were trying to insert data into the ID field which was set as an autonumber.
Now I'm at work so can't take a look at my DB and say anything. But when I will come back home I will take a look at it.
Edited: Try to read this one. I think this will help you