Error in Stored Procedure execution

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SQL-Server

I am trying to execute the following Stored Procedure for the Department table in my DataBase for which i am getting this error.
Msg 208, Level 16, State 6, Procedure Proc_Department_Select, Line 24 Invalid object name 'dbo.Proc_Department_Select'.

Can anybody help me with this?

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

ALTER PROCEDURE [dbo].[Proc_Department_Select] 
	@DepartmentID as int=null	
AS
BEGIN	
SET NOCOUNT ON;
IF (@DepartmentID is null or @DepartmentID=0)
BEGIN  
SELECT  d.DepartmentID,
	d.DepartmentName,
	d.PhoneNo
FROM Department d
END

ELSE
BEGIN
SELECT  d.DepartmentID,
	d.DepartmentName,
	d.PhoneNo
FROM Department d
WHERE d.DepartmentID = @DepartmentID
END
END
GO

I've been unable to locate the cause of the error and would appreciate all help..!!

Thank you.