Problem in verifying password from database stored in sha1 with salt

From my login page I want to store the credentials in encrypted format in the database.The password gets stored in the DB in encrypted format but the problem occurs while verifying the password.Everytime I give the password it shows error ”error verifying password”.I am giving the same password while signing up.Guys, help me out.
Here is the code:
public partial class _Default : System.Web.UI.Page
{
string constr=System.Configuration.ConfigurationManager.ConnectionStrings["LocalSqlServer"].ConnectionString;
    private static string CreateSalt(int size)
    {
        RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
        byte[] buff = new byte[size];
        rng.GetBytes(buff);
        return Convert.ToBase64S ...