One of the certificates installed inside the VPS is likely to be expired, preventing the connection.
It is necessary to delete the expired certificate using the command line.
1. Get a list of certificates from Remote Desktop store with this command:
It will output something like this, look for the certificate with the NotAfter date which has passed:
2. Delete the expired certificate with this command (replacing the bold serial number with your own of course):
It will output something like this:
The next time you connect via RDP a new self signed certificate should be created allowing you to login.
Article from:
http://kb.parallels.com/en/112975