Can anyone tell me why the update command works with Northwind and Adventureworks databases, but not with a database created by SQL express?

Question

I'm using VS 2008. I can't seem to get the update command to work with a database I created with SQL Express but yet it works with the Northwind and Adventureworks sample databases. Can anyone tell me why?
private void myTableBindingNavigatorSaveItem_Click(object sender, EventArgs e)
{
try
{
this.Validate();
this.myTableBindingSource.EndEdit();
this.tableAdapterManager.UpdateAll(this.myDataSet);
MessageBox.Show("Update successful");
}
catch (System.Exception)
{
MessageBox.Show("Update failed");
}
}