It is a permissions issue. For the Linux platform, you can "chmod" the file to 777 it should work...
[deric@noname deric]$ chmod 777 filename.txt
or you might want to set the ownership so that it gives the web server privileges to the file. You can check in phpinfo(); in the "User/Group" parameter. Although you'll have to be root on the box to perform the "chown" command. this will make it harder for people on a public box to see your files (although it's still very possible).
[root@noname deric]# chown user.apache filename.txt
Hope this solves your problem...