Not working, invalid form_build_id

I've enabled this module, followed the instructions, and cannot get it to work. Anytime I'm on a node and trying to add a comment (save or preview) I receive these errors:

* warning: array_shift() [function.array-shift]: The argument should be an array in sites/all/modules/ajax_comments/ajax_comments.module on line 115.
* warning: Invalid argument supplied for foreach() in sites/all/modules/cck/content.module on line 1278.

Not sure why content.module has issues as well.

A print_r of $_POST shows this:

Array
(
    [comment] => test
    [form_build_id] => form-e0d423bd281fecf46e73da90ebeb44e7
    [form_token] => 1ee08ff2c425aa33c9da8e70a897aaec
    [form_id] => comment_form
    [op] => Preview
)

And $form_state, after form_get_cache() is called is empty:

Array
(
    [storage] => 
    [submitted] => 
)

When I view the form cache table in the DB, there's no form_form-e0d423bd281fecf46e73da90ebeb44e7.