Data doesnt show on the GUI

Dear All,

I have a problem when key in the data in textbox. it doesnt show in textbox. 

Example i key in gross weight in textbox, it only show in NetWeight. For total Cost is empty.

 <asp:TableRow ID="TableRow8" runat="server" ForeColor="Teal">
             <asp:TableHeaderCell BorderColor="Black" BorderWidth="1" BackColor="#0C0C25" ForeColor="White">Gross Weight:</asp:TableHeaderCell> 
            <asp:TableHeaderCell BorderColor="Black" BorderWidth="1" Width="200" HorizontalAlign="Left" ForeColor="Red" BackColor="ControlLight">
                <asp:TextBox ID="WMGrossWeight" runat="server" RepeatDirection="Horizontal" AutoPostBack="True" OnTextChanged="CalNett_TextChanged"></asp:TextBox>
                
                 <asp:RequiredFieldValidator ID="WMGrossWeightRFV" runat="server" ErrorMessage="***"  ControlToValidate="WMGrossWeight" ValidationGroup="Add"></asp:RequiredFieldValidator>
            </asp:TableHeaderCell> 
    

            <asp:TableHeaderCell BorderColor="Black" BorderWidth="1" BackColor="#0C0C25" ForeColor="White">Net Weight :</asp:TableHeaderCell> 
            <asp:TableHeaderCell BorderColor="Black" BorderWidth="1" Width="200" HorizontalAlign="Left" ForeColor="Red" BackColor="ControlLight">
                <asp:TextBox ID="WMNetWeight" runat="server" ReadOnly="true" ForeColor="Blue"  ></asp:TextBox>
               
                 <asp:RequiredFieldValidator ID="WMNetWeightRFV" runat="server" ErrorMessage="***"  ControlToValidate="WMNetWeight" ValidationGroup="Add"></asp:RequiredFieldValidator>
            </asp:TableHeaderCell> 
            </asp:TableRow>




             <asp:TableRow ID="TableRow9" runat="server" ForeColor="Teal">
             <asp:TableHeaderCell BorderColor="Black" BorderWidth="1" BackColor="#0C0C25" ForeColor="White">SludgeWeight:</asp:TableHeaderCell> 
            <asp:TableHeaderCell BorderColor="Black" BorderWidth="1" Width="200" HorizontalAlign="Left" ForeColor="Red" BackColor="ControlLight">
                <asp:TextBox ID="WMSludgeWeight" ReadOnly="true" ForeColor="Blue"  runat="server"></asp:TextBox>
               
                 <asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server" ErrorMessage="***"  ControlToValidate="WMUnitCost" ValidationGroup="Add"></asp:RequiredFieldValidator>
            </asp:TableHeaderCell>

             </asp:TableRow>




             <asp:TableRow ID="TableRow7" runat="server" ForeColor="Teal">
             <asp:TableHeaderCell BorderColor="Black" BorderWidth="1" BackColor="#0C0C25" ForeColor="White">UnitCost:</asp:TableHeaderCell> 
            <asp:TableHeaderCell BorderColor="Black" BorderWidth="1" Width="200" HorizontalAlign="Left" ForeColor="Red" BackColor="ControlLight">
                <asp:TextBox ID="WMUnitCost" ReadOnly="true" ForeColor="Blue"  runat="server"></asp:TextBox>
               
                 <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ErrorMessage="***"  ControlToValidate="WMUnitCost" ValidationGroup="Add"></asp:RequiredFieldValidator>
            </asp:TableHeaderCell>
           


             <asp:TableHeaderCell BorderColor="Black" BorderWidth="1" BackColor="#0C0C25" ForeColor="White">TotalCost :</asp:TableHeaderCell> 
            <asp:TableHeaderCell BorderColor="Black" BorderWidth="1" Width="200" HorizontalAlign="Left" ForeColor="Red" BackColor="ControlLight">
                <asp:TextBox ID="WMTotalCost" runat="server" ReadOnly="true" ForeColor="Blue" ></asp:TextBox>
                  <asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ErrorMessage="***"  ControlToValidate="WMTotalCost" ValidationGroup="Add"></asp:RequiredFieldValidator>
            </asp:TableHeaderCell>         
        </asp:TableRow>

 protected void CalNett_TextChanged(object sender, EventArgs e)
        {

            float GrossWeight = float.Parse(this.WMGrossWeight.Text.Trim());
            float UnitCost = float.Parse(this.WMUnitCost.Text.Trim());
          
            float WDEGNettWeight = (GrossWeight - 85);
            float WDEGTotalCost = (WDEGNettWeight * UnitCost);


            float WGPNettWeight = (GrossWeight - 26);
            float WGPTotalCost =  (WGPNettWeight * UnitCost);




            if (WMItem.SelectedValue == "SW.307.004 ")

               this.WMTotalCost.Text = WDEGTotalCost.ToString();
               this.WMNetWeight.Text = WDEGNettWeight.ToString();



                if (WMItem.SelectedValue == "SW.422.001 ")

                   this.WMTotalCost.Text = WGPTotalCost.ToString();
                   this.WMNetWeight.Text = WGPNettWeight.ToString();

           

            }

        

When i debug, it show the correct data, Kindly advise, thank you