I've seen this same sort of thing but with eBay. They ask that you sign in using their link so that they get your Paypal address/password. I logged into my Paypal using a different browser and through the secure Paypal website and of course I found out that there is no open case.
Please keep your eyes open for similar scams.
As part of our security measures, we regularly screen activity in the PayPal
system. We recently contacted you after noticing an issue on your account.
We requested information from you for the following reason:
A recent review of your account determined that we require some additional
information from you in order to provide you with secure service.
Case ID Number: PP-751-840-288
This is a second reminder to log in to PayPal as soon as possible. Once you log
in, you will be provided with steps to restore your account access.
Be sure to log in securely by using the following link:
Click here to login and restore your account access