I am having the same problem as mentioned in this thread :
http://wordpress.org/support/topic/falcon-activation-problem-and-a-workaround . When enabling (or subsequently disabling) the cache I get this error:
Problem disabling caching.
We could not disable caching because you have code in your .htaccess file that could not be removed by Wordfence. You need to go in and remove any Wordfence code from your .htaccess file yourself. Then return here and disable caching. The error we received was: fopen(/path/to/blog//.htaccess) [function.fopen]: failed to open stream: Permission denied
My htaccess permissions are
-rw-r--r-- 1 root root 487 Aug 2 2013 .htaccess
Any idea of changing ownership of the htaccess file (or group) might help?