Compiler Error Message: CS0246: The type or namespace name could not be found (are you missing a using directive or an assembly reference?)

 hai all
                   i'm getting the following error when i hosted my website. However its working in local machine

Compiler Error Message: CS0246: The type or namespace name 'DA' could not be found (are you missing a using directive or an assembly reference?)
where DA is a class in App_Code folder...it is not a dll..but a simple class
see my code that caused error
Line 22: string[,] Params = new string[2, 2] { { "@agentid", usrname.Value }, { "@pwd", pwd.Value } };
Line 23:
Line 24: DA myDA = new DA();
Line 25: SqlDataReader dr = myDA.DRStrProc("agent_login", Params);
 
why i'm getting this error ...