Viewing uploaded PDF files

I have an appication where users need to be able to view PDF files. Using ASPRunner's file upload function, the files upload fine. However, The resulting PDF links do not always work. Any other file type does. I usually get the dialog box for opening or saving. But PDF files are volatile. Internet Explorer simply says that the page cannot be displayed. Google just sits there waiting. But FireFox says, "File not found. Firefox can't find the file at http://swclients2.ridgways.com/demo/admin/JobArchive_download.asp?field=PDFPreview&key1=1151."; In testing, it seems to have something to do with the size of the PDF, although file size does not matter for links to other file types. a 1 MB PDF file will open but a 7 MB PDF file won't.