File Upload Control does not have the file

I have a form where the user clicks on browse of the file upload control and selects a file.  Then when they click submit the control thinks they havn't selected a file when they have.  This only happens on the production server.  Test server and development environment both work perfectly.  It's a C# ASP.NET web app running on a Windows 2003 Server os.  Here is a piece of the server side code, everytime the event fires and the FileUpload1 checks the HasFile property it is returning false even if the user selects a file:

protected void Button1_Click(object sender, EventArgs e)
    {
       
        if (FileUpload1.HasFile)
        {
            lblResult.Visible = false;
            ...