please check on theme folder..
make sure there's folder named "cache" and permission is 777
you can do it by login using filezilla..
and go to wp-content/themes/THEMEFOLDER
and right click -> create folder, named with "cache"
after this right click folder "cache" -> change permission -> type "777"
if you still got error, please submit ticket and give your url
so we can check directly to your site