Sorry , i also find the same problem ....
i want to use stored procedure to do this , but also same problem....
my code is... (in this the program said the returnValue can not 'System.Int32' convert to'System.Byte[], but i use the VarBinary ,it also change to int,
         Is not StoredProcedure return value must integer , then how can i do, thx~~~?)


Dim sqlCmd As New SqlCommand

        sqlCmd.Connection = cn
        sqlCmd.CommandType = CommandType.StoredProcedure
        sqlCmd.CommandText = "dbo.sp_encrypt"
        Dim inputValue As SqlParameter = sqlCmd.Parameters.Add("@word", SqlDbType.NVarChar)
        inputValue.Value = Adjust_SQL(TextBox1.Text)
        Dim ReturnValue As SqlParameter = sqlCmd.Parameters.Add("ReturnValue", SqlDbType.VarBinary)
        ReturnValue.Direction = ParameterDirection.ReturnValue
        sqlCmd.ExecuteNonQuery()
        Dim hex As String = "0x" + BitConverter.ToString(ReturnValue.Value).Replace("-", "")  
    < in this the program said the returnValue can not 'System.Int32' convert to'System.Byte[], but i use the VarBinary ,it also change to int,
         Is not StoredProcedure return value must integer , then how can i do, thx~~~?)
        TextBox1.Text = hex