I had that same issue.I can't link my GC key with my account, I've tried several times and I'm tired, I will probably receive my passport tomorrow via DHL, estimated time was 31st August.... I'm tired of stressing.
There is a question "how many people are on this application" or something like that... I kept using "1" and so couldn't link. Just change your response to "2". Cos it adds your spouse and yourself as 2 people for the application.
Try that and see if you can link it.