Okay, the error your getting means that fopen can't open the file you're requesting because the permissions of that file (or directory) won't allow it.
If you're server is on Linux:
From the shell cd to the directory where that file resides, and issue
chmod 777 *
This will give you full read/write/execute permissions to all files in the directory, and prevent the error from occurring again.
If you're running your site from a web host, check with them for how to change your permissions.