We got the security notice today and upgraded our system to 5.1.4. It was working fine but noticed WHMCS still said there was an update available and found out 5.2.1 is now stable. We upgraded to 5.2.1 using the instructions (extract, rename admin folder, backup database, upload and overwrite files/folders). Now admin account can no longer log in, saying invalid password. Using the Forgot Password link, we enter the admin email address, get the link to reset the password, and we get the error "Invalid or Expired Link Followed. Please try again.". Tried it a couple more times, each link causing the same error.
So we tried to log into a user account, still got an invalid password. Did the reset password link on that page, got the email, clicked it, this time it says "Password Reset Successful" but we do not get an email telling us what the new password is.
Been trying to enter a ticket but when we submit the ticket, we get the error:
Service Temporarily Unavailable
The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.