System.IO.File.Exists And set IIS

Hi all.

I want Check file exists in SharePoint webpart.

So I found class the System.IO.File.Exists.

---source---

string path = @"\\nar-cla500s3\memo\test\skill\print-001.xls";  <-- return only false
            try
            {
                if (System.IO.File.Exists(path))
                    Label.Text = "true";
                else
                    Label.Text = "false";
            }
            catch { }

----source-----

If i wirte LocalPath(@"C:\memo\test\skill\print-001.xls), I Can get True.

My all APP's processID is win\lx13040020, And win\lx13040020 can access <\\nar-cla500s3\memo\test\skill\print-001.xls>

But I got only false...

is this double hope problem? I want check exists from file server.

I need your help, Thank you.