When the new Critical Update is activated in our Sandbox organization, we get the following error on every non-managed visualforce page:

<DomainName>--c.visualforce.com's server IP address could not be found.

We left it overnight in case it was an issue with the DNS not being updated, but that doesn't seem to be the case. Deactivating the update restores all functionality. Does something else need to be updated in order to get our non-managed pages working?

Thank you.