Dropdownlist in gridview reset to Default Instead of selected value - asp.net

Question

I have two GridView(SalesGView and ProdGView). SalesGView contains dropdowlist and textboxes.ProdGView is wrapped with ModalPopup and is populated by dropdownlist selection from ProdGView.
The issue is when i click button select on ProdGView, the dropdownlist in the SalesGView resets to default value (Electronics) instead of selected value.
I need help on how to correct this issue.
aspx code:
SalesGView Dropdownlist
<asp:DropDownList ID="CatCode" OnSelectedIndexChanged ="CatCode_SelectedIndexChanged" AutoPostBack="true" runat="server" />
ProdGView SelectRow
<asp:GridView ID="ProdGView" runat="server" AutoGenerateColumns="False">
<Columns>
<asp:TemplateField>
<ItemTemplate>
<asp:Button ID="btnSelect" Text="Select" runat="server" OnClick="SelectRow" />
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
Code Behind:
Private Sub SalesGView_RowDataBound(sender As Object, e As GridViewRowEventArgs) Handles SalesGView.RowDataBound
If (e.Row.RowType = DataControlRowType.DataRow) Then
Dim ctrl As Control = e.Row.FindControl("CatCode")
If (Not (ctrl) Is Nothing) Then
Dim dd As DropDownList = CType(ctrl, DropDownList)
Dim connStr As String = ConfigurationManager.ConnectionStrings("SY_InventoryConnectionString").ConnectionString
Dim sqlda As SqlDataAdapter = New SqlDataAdapter
Dim com As SqlCommand = New SqlCommand
Dim dt As DataTable
Dim conn As SqlConnection = New SqlConnection(connStr)
dt = New DataTable
com.Connection = conn
com.CommandText = "SELECT CatName FROM Prod_Category"
sqlda = New SqlDataAdapter(com)
sqlda.Fill(dt)
dd.DataTextField = "CatName"
dd.DataValueField = "CatName"
dd.DataSource = dt
dd.DataBind()
End If
End If
Dim lb As DropDownList = TryCast(e.Row.FindControl("CatCode"), DropDownList)
ScriptManager.GetCurrent(Me).RegisterAsyncPostBackControl(lb)
End Sub
Protected Sub CatCode_SelectedIndexChanged(sender As Object, e As EventArgs)
Me.ModalPopupExtender1.Show()
BindProdGrid()
End Sub
Protected Sub SelectRow(sender As Object, e As EventArgs)
Dim dt As New DataTable()
If ViewState("DataTable") Is Nothing Then
dt = New DataTable()
dt.Columns.AddRange(New DataColumn(1) {New DataColumn("Column2"), New DataColumn("Column4", GetType(String))})
Else
dt = DirectCast(ViewState("DataTable"), DataTable)
End If
Dim row As GridViewRow = TryCast(TryCast(sender, Button).NamingContainer, GridViewRow)
Dim desc As String = row.Cells(2).Text
Dim price As String = row.Cells(3).Text
dt.Rows.Add(desc, price)
Me.SalesGView.DataSource = dt
Me.SalesGView.DataBind()
ViewState("DataTable") = dt
End Sub
Private Sub BindProdGrid()
Dim conString As String = ConfigurationManager.ConnectionStrings("SY_InventoryConnectionString").ConnectionString
Dim rowIndex As Integer = 0
Dim catname As DropDownList = CType(SalesGView.Rows(rowIndex).Cells(1).FindControl("CatCode"), DropDownList)
Using con As New SqlConnection(conString)
Using cmd As New SqlCommand("select Product.CatID,Product.PName,Product.PDesc, " _
& " Product_Details.USP, Prod_Category.CatName " _
& " from Product inner join Product_Details on Product.CatID= Product_Details.CatID " _
& " inner join Prod_Category on Product_Details.CatID=Prod_Category.CatID where Prod_Category.CatName='" & (catname.SelectedItem.Text) & "' ")
Using sda As New SqlDataAdapter()
cmd.Connection = con
sda.SelectCommand = cmd
Dim dt As New DataTable()
sda.Fill(dt)
Me.ProdGView.DataSource = dt
Me.ProdGView.DataBind()
End Using
End Using
End Using
End Sub