This issue happens intermittently and I have customers call me there's an issue and on my end everything works fine. Until I tested it myself today was able to replicate the problem.
When someone tries to start a subscription on the site at the page.
They get this popup.
In the network tools dev console, it runs this script
members.xxxxxxx.net/cb-profile/saveregisters
Then I close the browser and I can subscribe successfully the next time.
CB version is 2.4.6
CB Paid Sub version is 4.1.0+build.2016.09.20.07.58.14.931a0995b
Thanks!