Writing to Mapped Drive : Permission Denied

Warning: fopen("U:\filename.txt","w+") - Permission denied in D: \wwwroot\somepath\more\thescript.php I'm having this terrible problem writing a file to a drive that is mapped by the server. I'm not even sure its a PHP problem, but my perl scripts don't seem to have any trouble with it. IIS 5, PHP 4, Win2k The script runs under a virtual directory that has NT Authentication checked, Anonymous Access unchecked [so the REMOTE_USER server variable is available to the php scripts]. The drive is mapped to a folder on another server that gives Guest and Everyone "Full Control". If you run the script from the server [from the servers web browser], it works perfectly. The server is logged in as Domain Admin, but no matter how I try to access the script from a workstation - even as Domain Admin, I still get an error. I am able to write files to the mapped directory from a workstation using explorer. When Anonymous Access is on, it works fine but I am unable to use the REMOTE_USER variable. Is there a way to write files to a mapped directory with "Anonymous Access" turned off? Thanks in advance, -Paul Wieland