CTools CSS Cache Error on Status Page
The "files" directory of your installation (usually located at sites/default/files) must be writable by user the execute the server (Apache, for example).

So, if you have access to a console could try:

sudo chown -R www-data:www-data sites/default/files (for Ubuntu or Debian)
sudo chown -R apache:apache sites/default/files (for Centos or Redhat)