Make sure that your Ledger device is running the most recent version of the Tezos wallet app. This can be installed via Ledger Live on your device. Verify that no other applications are connected to the Ledger device while running Galleon. These include Ledger Live, other wallets or websites that my interact with it. Quit Galleon and attempt the following in the exact order:
- Plug in and unlock your Ledger device.
- Open the Tezos wallet app on your Ledger.
- Start Galleon
- Click on the “Connect with Ledger” button and respond to the prompts on your Ledger device.
If you are still unable to connect your Ledger device after doing so, follow the troubleshooting instructions for connecting a Ledger device here. The most common cause of this issue is related to "udev" rules on Linux.