Incorrect syntax near '+'.

Question

        GO

/****** Object:  StoredProcedure [dbo].[Add_Result]    Script Date: 08/30/2011 12:24:44 ******/

SET ANSI_NULLS ON

GO

SET QUOTED_IDENTIFIER ON

GO

CREATE PROCEDURE [dbo].[Update registerno]

(

@filename nvarchar(50),

@sheetname nvarchar(50)

)

AS

BEGIN

UPDATE StudentRegistration SET adno = T.[adno]  

FROM OPENROWSET('Microsoft.ACE.OLEDB.12.0', 'Excel 12.0;Database=' + @filename + ';HDR=YES', 'SELECT * FROM [Sheet1$]')T  

WHERE StudentRegistration.regno = T.[regno]

END

        The following error occur in above sql query

Msg 102, Level 15, State 1, Procedure Update registerno, Line 12

Incorrect syntax near '+'.