That error message suggests that there may be a short term problem inside the systems operated by Bitcoin.io, in which case I would just retry every day or so.
Clause 5.1.2 of their user agreement says
When you create a Wallet, the Wallet software generates a cryptographic private and public key pair that you may use to send and receive any supported Virtual Currency via the relevant Virtual Currency network. You are solely responsible for storing, outside of the Services, a backup of any Wallet, private key or transaction information that you maintain in your Wallet or otherwise with the Services. If you do not maintain a backup of your Wallet data outside of the Services, you will be may not be able to access Virtual Currency previously accessed using your Wallet in the event that we discontinue or no longer offer some or all of the Services or may otherwise lose access to Virtual Currency. We are not responsible for maintaining this data on your behalf.
If you have the private keys in a known format, you should be able to import them or sweep them into a normal Bitcoin wallet
Please read about the advantages and disadvantages of importing vs sweeping and differences between full-node and SPV wallets.