Your header states its a Linkstation Live 500gb (HS-DH500GL).
Your text states that its a Linkstation Gigabit (HS-DGL).
You are trying to upgrade a Linkstation Live by using a Linkstation Gigabit firmware, it will not work.
Re-confirm your model again by looking at the Buffalo product.
If it is a Linkstation Live mode, then download the appropriate firmware for it.
Try not to go thru a switch when upgrading the firmware.
Do it directly from the Buffalo unit connected to a Computer.
If your Linkstation is not statically configured, then you will likely get a default IP.
You can easily see this default IP when after the Linkstation has booted up and running the NAS Navigator software.
Once you see the IP, configure your Computer to match the IP range of the Linkstation.
Then you can proceed to update the Linkstation.