Reading a file on a remote server

Hi, I'm trying to read a file on a remote server from my webpage and am having real problems !
My code is:
filetoread = Server.MapPath("\\servername\share\file.csv")
        filestream = File.OpenText(filetoread)
        readcontents = filestream.ReadToEnd() 
It works fine if I put the file in the local directory and use "filetoread = Server.MapPath("file.csv")", but won't do it over the UNC path.
I'm guessing the problem is security related but can't find any info related to it, do I need to somehow specify a username/password somewhere ?

 
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