Can "Download" but not "View"

I have set BaseDir and BaseUrl in my config.ascx:

BaseUrl = String.Format("{0}/{1}", Website.Models.Globals.FileUploadUrlBase, (string)Session["user"]);

        BaseDir = String.Format("{0}\\{1}", Website.Models.Globals.FileUploadBase, (string)Session["user"]);

These resolve to, for example,

/Upload/2013/foo-bar

c:\path\to\Upload\2013\foo-bar

And I can upload files and right-click and download the files, but if i right-click to view the file, the "/Upload/2013" is not included in the URL and therefore I get a 404. I'm probably just missing a configuration setting, but I can't figure out what that is.