Localization :: Google Caches Error 404 Page For Localized Website?

I have an ASP.Net(2.0) website which I have localized based on user's browser settings. So when a user navigates to my website, I check their browser settings and redirect them.Here's the code which I have in global.asax

protected void Session_Start(object sender, EventArgs e)
{
string localeName = ResourceHelper.GetCulture();
string refUrl = HttpContext.Current.Request.Url.ToString();[code]....

My problem is that on google, my 404 error page is being cached and the error page title comes up as the search result.I think because of the way I redirect users, the search crawler gets to the error page instead of the homepage.