We have a few people using Plesk 10, and there has been one notable bug with new installs and upgrades.
Plesk has decided to redirect after the login to the server https://hostname:11444/relay

Whilst this is fine if your hostname is a valid domain name that points to your server, this can be problematic for new setups or similar.

There are a couple of fixes, the best one is to change your hostname to be a valid domain name that points to your server. You can do that by editing /etc/hostname and rebooting, however this may not pickup so you may need to set it up with

/usr/share/plesk-billing/update-hostname --new-hostname=newdomain.com

Alternatively you can use an IP in this field ie

/usr/share/plesk-billing/update-hostname --new-hostname=207.210.xxx.xx