Form Key Error when removing a product from Mini cart

You have two options,

1. Disable form keys for the remove action.

   There is no real risk in doing this, the CSRF protection the form keys add have limited scope for damage when removed on cart actions. You could use this module as a basis if you wanted to script something

2. Change the remove link to use

   getUrl('checkout/cart/ajaxDelete', array(..., Mage_Core_Model_Url::FORM_KEY => $this->_getSingletonModel('core/session')->getFormKey()));
   

Turns out that it was merging my files with the Fooman extension.

I restored my installation to a day before installing the extension and the problem is gone. Thank you Natalie for the nudge in the right direction.

What I have done instead is pretty great I think, and something I'd like to mention here for others in the future. I installed Fishpig's module Opti that minifys the js and css files, and then I installed a module by Gordon Lesti that merges the files much smarter than Magentos own method.

Please read here:

https://gordonlesti.com/projects/lestimerge/

http://fishpig.co.uk/magento/extensions/minify/

For me the problem was related to having taken off the remove class from the remove button. You either need to revert this change or change the selector in skin/frontend/<rwd>/default/js/minicart.js on line 32 to correctly target your remove button.