Fatal error: require() [function.require]: Failed opening required in wordpress

Check the permissions of the functions.php.

This page in de Codex about changing file permissions explains a lot about wich permissions you have, or can use.

On computer filesystems, different files and directories have permissions that specify who and what can read, write, modify and access them. This is important because WordPress may need access to write to files in your wp-content directory to enable certain functions.