Returning a null Reference Exception

 public void S开发者_高级运维chemeUpdate(int SchemeID, int InsurerID, string Name, string Description)
        {
            Health_Scheme_System.Scheme updscheme = Scheme.Find(x => x.SchemeID == SchemeID).FirstOrDefault();

            //updscheme.SchemeID = SchemeID;
            //updscheme.InsurerID = InsurerID;
            updscheme.Name = Name;
            updscheme.Description = Description;                             
            updscheme.Save();
}


Calling the method


  //Converting to integer and date
                    int SchemeID;
                    int.TryParse(txtSchemeID.Text, out SchemeID);

                    int insurerID;
                    int.TryParse(txtInsurerID.Text, out insurerID);


                    //Getting the parameters from the method
                    DataAccess updscheme = new DataAccess();
                    //DataAccess updrates = new DataAccess();
                    updscheme.SchemeUpdate(SchemeID, insurerID, txtName.Text, txtDescription.Text);
                    //updrates.RatesUpdate(SchemeID, txtRates.Text);

                    //Binding the gridView to display the updates
                    txtSchemeID.Visible = false;
                    txtInsurerID.Visible = false;
                    gvSchemeMain.DataSource = ds.GetRates();
                    gvSchemeMain.DataBind();

I think the problems is with the parameters..

Based on your comment it looks like this line:

Health_Scheme_System.Scheme updscheme = Scheme.Find(x => x.SchemeID == SchemeID).FirstOrDefault();

is not returning anything. In other words, there is no Scheme with an ID of whatever you're using.

Can you manually check in the database for a Scheme and get it's ID value. You can then test the above code by passing that value into the SchemeID parameter.