Transferring ID from CLI version

Anyone know how to get the “private key string” from a wallet.json file?
I’m trying to transfer my ID from the old Blockstack cli version to the new Blockstack browser but I get stuck on the following message:
optional: A private key string to be used for the update. (“owner_key”):

You’ll need the old CLI to do this. First, you run blockstack wallet to get your current owner private key. Then, you use the new CLI to do the transfer (use blockstack-cli help transfer for an example).

What do you mean by “old CLI”? I am already running the older Which version should I be running? And when running the “blockstack wallet” command, I get the following:
“error”: “Failed to save keys”

I need some help with this as well. Installing blockstack-client on a fresh 2.7 virtualenv fails with: ImportError: cannot import name tx_serialize