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