Getting a legacy wallet back

I'm trying to move a wallet from 2012 using bitcoin-qt. I kick off the migration, put in my password, and then I get hit with this error: "Error: Unable to read wallet's best block locator record". I can't seem to find anything about this error anywhere. Any tips?

Are you on the latest bitcoincore?

Looks like it doesn't have the record of the last block or blockchain tip when it's last synced for some reason. Try v29.0 (it supports legacy wallets), use "Restore Wallet", let it sync. After syncing, backup the synced restored wallet file via "Backup Wallet" to create an extra copy and then migrate. If successful, update your Bitcoin Core to the latest version.

Stop and don't retry that migration yet. If you're on Core 30.0 or 30.1 there's a known bug where a failed legacy wallet migration can wipe everything in the wallet dir. First thing: copy your wallet.dat somewhere safe (ideally offline) before touching anything else. Once it's backed up, easiest safe route is to extract the keys without migrating. I would go with a pywallet dump.

Even without knowing about that bug, it's always highly recommended that people must make multiple copies (backups) of a wallet file, before starting to do any wallet recovery attempt. Be more careful means vital for your fund, because if the only wallet backup is broken, you will lose your bitcoin forever. [overview] Recover Bitcoin from any old storage format.

This is a known issue that will be fixed in the next major version of Bitcoin Core.