I have restarted apache (and even the whole server) and it didn't help. Additionally, I ran the code you suggested and that didn't help either. I also ran:
root@ispconfig3:~# chown web35:client10 /var/clients/client10/web35
root@ispconfig3:~# chown -R web35:client10 /var/clients/client10/web35/web
root@ispconfig3:~# chmod -R 755 /var/clients/client10/web35/web
To make sure all files were rwx by the web35 user. This didn't help either.