The variable name '@' has already been declared & must declare scalar variable @

I want to insert data from DataGridView to the database by using sqlparameters and for loop:

Dim sqlAddCmd As New SqlCommand

sqlAddCmd.CommandText =
                        "INSERT INTO TableName (Val,Idx,Ref,Sta,Col,Point,Mat,Refer,Cover,IDNo,Mas)" _
                            & "VALUES (@Val,@No,@Ref,@Sta,@Col,@Point,@Mat,@Refer,@Cover,@IDNo,@Mast)"

            sqlAddCmd.Transaction = transaction

            With sqlAddCmd.Parameters
                .Add("@Val", SqlDbType.Int)
                .Add("@No", SqlDbType.TinyInt)
                .Add("@Ref", SqlDbType.Char)
                .Add("@Sta", SqlDbType.Char)
                .Add("@Col", SqlDbType.VarChar)
                .Add("@Point", SqlDbType.SmallInt)
                .Add("@Mat", SqlDbType.VarChar)
                .Add("@Refer", SqlDbType.Int)
                .Add("@Cover", SqlDbType.TinyInt)
                .Add("@IDNo", SqlDbType.VarChar)
                .Add("@Mast", SqlDbType.Char)

            End With

            For intI = 0 To daGridView.Rows.Count
                With sqlAddCmd
                    .Parameters("@Val").Value = lngNewID
                    .Parameters("@No").Value = daGridView.Rows(intI).Cells("dgvNo").Value
                    .Parameters("@Ref").Value = daGridView.Rows(intI).Cells("dgvRef").Value
                    .Parameters("@Sta").Value = daGridView.Rows(intI).Cells("dgvSta").Value
                    .Parameters("@Col").Value = daGridView.Rows(intI).Cells("dgvCol").Value
                    .Parameters("@Point").Value = daGridView.Rows(intI).Cells("dgvPoint").Value
                    .Parameters("@Mat").Value = daGridView.Rows(intI).Cells("dgiMat").Value
                    .Parameters("@Refer").Value = daGridView.Rows(intI).Cells("dgiRefer").Value
                    .Parameters("@Cover").Value = daGridView.Rows(intI).Cells("dgiCover").Value
                    .Parameters("@IDNo").Value = daGridView.Rows(intI).Cells("dgiIDNo").Value
                    .Parameters("@Mast").Value = daGridView.Rows(intI).Cells("dgiMast").Value
                End With
                sqlAddCmd.ExecuteNonQuery()
            Next

But when I want to insert this it will show the error code

> The Variable Name @Val has already been declared. Variable must be unique within a query batch or stored procedure.
> Must declare the scalar variable @No.

I know the val must be unique so I do that based on what the others suggest but still get the problem like this. Is there something missing?

I got the answer. The problem is I already use the @Val parameter. So I create new Parameter called @ValDG. And then instead of using For ... Loop,
I use Do ... While. So the code is like this:

intI = 0
Do While intI <= datagrid.Rows.Count - 1
sqlcommand.commandText = "INSERT INTO TableName (Val,Idx,Ref,Sta,Col,Point,Mat,Refer,Cover,IDNo,Mas)" _
                        & "VALUES (@ValDG,@No,@Ref,@Sta,@Col,@Point,@Mat,@Refer,@Cover,@IDNo,@Mast)"
sqlcommand.Transaction = transaction

With sqlcommand.parameters
    .Add("@ValDG",SqlDbType.int).Value = lngNewID
    .....
End With
sqlcommand.ExecuteNonQuery()
intI +=1
Loop

I hope it will help. Sorry for the late answer post.