Im getting an error as like object reference not set to an instance of an object.

<asp:FormView ID="fvFileUpload" runat="server" Width="418px">
        <ItemTemplate>
            <asp:Label ID="lblFileId" Text="File ID" runat="server" Width="120px" />
            <asp:TextBox ID="txtFileID" runat="server" />
            <br />
            <asp:Label ID="lblFileName" Text="File Name" runat="server" Width="120px" />
            <asp:TextBox ID="txtFileName" runat="server" />
            <br />
            <asp:Label ID="lblFileKey" Text="File Key" runat="server" Width="120px" />
            <asp:TextBox ID="txtFileKey" runat="server" />
            <br />
            <asp:Label ID="lblUpload" Text="File Upload" runat="server" Width="120px" />
            <asp:FileUpload ID="fupload" runat="server" />
            <br />
            <asp:Label ID="lblUplodedBy" Text="File Owner" runat="server" Width="120px" />
            <asp:TextBox ID="txtOwner" runat="server" />
            <br />
            <br />
            <asp:Button ID="btnReq" Text="Requset to Auditor" runat="server" OnClick="btnReq_Click" />
            <asp:Button ID="btnClear" Text="Clear" runat="server" Height="25px" OnClick="btnClear_Click" Width="150px" />
        </ItemTemplate>
    </asp:FormView>

private void FileIDGen()
   {
       string FileID = crudobj.SelectFileId();
       ((TextBox)fvFileUpload.FindControl("txtFileID")).Text = FileID; // im getting error here but im getting FileId string value as File1. the problem occurs when it tries to assign that value to the textbox
   }