PC Plus accounts have been compromised. Thieves have been logging into accounts with weak passwords, setting up a new card number on your account and using the points. This is likely the reason behind the move to no longer allow redemptions of gift cards as they are generally the easy option for thieves.
New passwords must be 8 characters, plus include an upper case letter and number. You will not be able to log in until you update your password. If you cannot find the email from them, simply go to the PC Plus homepage, and click forgot my password and they will send you a new link.