Failed to open stream – class-page-cache.php

I am getting a repeated error in my apache logs since installing this plugin – looks to be on every page load. What is wrong / how can I fix this?

`[date] [proxy_fcgi:error] [pid ####:tid ###] [client ###:###] ###: Got error ‘PHP message: PHP Warning: fopen(/…/htdocs/domain/wp-content/wphb-cache/cache/www.domain.co.uk/index.html): failed to open stream: No such file or directory in /…/htdocs/domain/wp-content/plugins/hummingbird-performance/core/modules/class-page-cache.php on line 881’

Thanks