Looks like your server don’t give permission to PHP script for write/delete files on server. Solution is to chmod 755 in following files/folders:

/templates/{your-template}/assets/cache and all files inside
/files/thumbnail and all files inside
/files/captcha and all files inside
/files and all files inside
/application/config/cms_config.php
/application/config/production/database.php
/application/language and all files/folders inside
/system/language and all files/folders inside
/templates/bootstrap2-responsive/language and all files/folders inside
/templates/bootstrap2/language and all files/folders inside
/application/logs and all files/folders inside
/sitemap.xml

If doesn’t help, you can try with chmod 777