18t8drSrz9GPTf7ahbj72hjrSpakQZZLYN is the address the bitcoins are. It was used for cold storage
It looks like there should be 5 unspent outputs that can be swept.
Are you certain you are sweeping the correct private key? If you are, then it sounds like blockchain.info may be having an issue at the moment. You might need to contact their support. You can try sending a PM to Piuk.