Warning: array_merge(): Argument #1 is not an array in _authcache_shutdown_save_page() (line 272 of authcache/authcache.helpers.inc).

I enabled the module
I enabled items in settings per D7 readme
I get the above

Comments

hmm, that's odd.

could you add the following line of code to authcache/authcache.helpers.inc line 261, and then tell me what output you get.

print '$_authcache_info<pre>'; var_dump($_authcache_info); print '</pre>'; die();