Nenkin Net Linking Error

I've been trying to get access to Nenkin Net after I received some pension information by mail.

I've managed to download the dreaded MynaPortal but every time I hit 'confirm' when trying to align/link it to Nenkin Net I first get 「ねんきんネットとの連携 – 連携待ち」 (waiting for alignment) which quickly becomes 「エラー」 (error) with no explanation.

Is there some trick I need to know to get this to work? I'd appreciate any help.