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

Source Error:

Line 13: using System.Data.Sql;Line 14: using System.Data.SqlClient;Line 15: using farhaniPersianDate;Line 16: Line 17: public class SDKClass
Source File: c:\Inetpub\wwwroot\2\Final Forum Project\Final Forum Project\Final Forum Project\App_Code\SDKClass.cs Line: 15