SQL Server 2008 Error: Saving changes is not permitted

Few days ago I have migrated one of my Database from SQL Server 2005 to SQL Server 2008. Actually what I did during migration? I have created a Database first in SQL Server 2008. Then I have imported all of my SQL Server 2005 tables into the SQL Server 2008 Database. I thought that Everything is perfect but when I live my application for testing then I found that System can not insert data into