server.mappath IE vs Firefox

[byrdman]

Im developing a web app in asp.net 2.0 with c#. Users upload images and I'm useing server.Mappath to put the images in a folder on the server while putting the file name in the database. My problem is everything works great in IE but not in Firefox. In Firefox when a user tries to upload a image it always asks for a username and password while IE processes the upload successfully.
Ive tried other methods as well that work in IE but not Firefox

FileUpload1.SaveAs(Server.MapPath(".") + "\\DLimages\\" + filename);

Looking for solutions.
Thanks

Richard