Indeed. I redeemed another PC Gamer key and now the client started patching. This is a huge mistake by Cryptic - if some of the redeemed keys are not working then there's a huge amount of accounts that haven't been activated for the beta. This means plenty of frustration for those people. :(
Three of my friends have all the same problem. They all redeemed PC Gamer keys, yet they are not able to patch the client and instead are getting the account error message. I had hoped this issue would be sorted out as it's already very close to the beginning of the beta :(