'cache_class_cache_page' bin doesn't work with filecache

Hi,

I'm using the Cache Backport module on Drupal 6 with File Cache. I'm trying to set up caching for the 'cache_class_cache_page' bin because I don't have enough memory to cache pages with something like memcache or Redis. But when I enable the 'cache_class_cache_page' bin, I get this error when I create a new node:

Warning: include_once(./includes/unicode.entities.inc) [function.include-once]: failed to open stream: No such file or directory in /home/myuser/webapps/drupal_6/includes/unicode.inc on line 339

Warning: include_once() [function.include]: Failed opening './includes/unicode.entities.inc' for inclusion (include_path='.:/usr/local/share/pear53') in /home/myuser/webapps/drupal_6/includes/unicode.inc on line 339

Thanks for the help!