We're very sorry about the problems this issue has caused for all of you. We understand how upsetting it is to be locked out of your sites/accounts.
To get the best support possible, I ask that each of you email email@example.com for one-on-one assistance.
As for the error "The application secret key passed to sign_request() must be at least 40 characters.", this key is the output of wp_salt(), which should always be well over 40 characters if the default wp_salt function is being used.
Some plugins can replace the wp_salt function, causing it to return unexpected values, potentially weakening the security of your site. For assistance in finding the offending plugin, please email firstname.lastname@example.org
P.s. For those that have asked, we perform extensive testing on a number of popular hosts, with many popular plugins, to mimic as wide a range of our customers as possible. We also work with select customers, directly, to beta test new versions of our plugin before general release.
If any of you are interested in beta testing (with the assistance of an Engineer live on the phone through the entirety of the installation!) please email us at email@example.com and let us know that you'd like to help! We have some openings right now that we would love to get filled!