Migration Assistant can't find my external hard drive

I'm trying to set up my Mac Mini and it isn't working. Three steps into the process and already I'm locked up. I'm trying to migrate data from an external FireWire 400 drive. I have to use an adapter because the Mini only has a Firewire 800 port. That's not a problem because I've used the adapter several times and it works fine. The external drive is connected directly to the Mini and turned on. It's been turned on before I went into this mode. Now the Migration Assistant is hung up on Select The Source with a spinning circle and the Continue button is greyed out. I don't want to bypass this step and do everything manually because that's a nightmare and with my schedule it will likely drag out for months.

Can anyone help?