You haven't returned anything from the routine (needs to return an int value)
public int insertlogin(DataContainer objdc,string CmdText)
{
Util.Open();
SqlCommand Cmd = new SqlCommand();
Cmd.Parameters.Clear();
Cmd.Connection = Util.SqlCon;
Cmd.CommandType = CommandType.StoredProcedure;
Cmd.CommandText = CmdText;
Cmd.Parameters.Add("@id", SqlDbType.Int).Value = objdc.id;
Cmd.Parameters.Add("@username", SqlDbType.VarChar, 50).Value = objdc.username;
Cmd.Parameters.Add("@password", SqlDbType.VarChar, 50).Value = objdc.password;
Cmd.ExecuteNonQuery();
Util.Close();
int loginReturnValue = 0;
return loginReturnValue;
}