I've been seeing the following error when using the Recurring Billing tools in sandbox (account is W3W3Q45W9798Y):
We are sorry, we are experiencing temporary difficulties. Please try again later. If this error occurred while making a payment, avoid duplicate payments by checking your Account Overview before resending a payment.
For some browsers, this problem can be resolved by clearing or deleting cookies.
I've tried clearing cookies, to no avail.
These steps seem to reproduce it reliably:
1. Open Tools > Recurring Payments > Create a Subscription button
2. Choose a button type of "Automatic Billing"
3. Click the "Learn more" button that has appeared in the form
(What I was actually trying to do if you're interested, is enable automatic billing through this link which I think should let me agree to the Ts and Cs)