Stripe is throwing a server error when trying to access a webhook to the Charge plugin. Some investigation revealed the error is triggered by an 'invalid or missing CSRF token.
If CSRF protection is enabled (and it is by default for the latest versions of Craft), Stripe was getting a server error when using the Charge webhook url. The solution is to disable CSRF for the webhook URI - you can read more about it here
or simply add this to your
'enableCsrfProtection' => (!isset($_SERVER['REQUEST_URI']) || $_SERVER['REQUEST_URI'] != '/actions/charge/webhook/callback'),