You never know what's on a hard drive until you check. Tablo may have created a partition the first time it tried to format the drive and then failed. I recommend deleting the partition again, and then:
01). Verify the Tablo is running the latest firmware.
02). Wait until the Tablo completely finishes downloading the Guide.
03). Verify the latest version of Chrome is installed.
04). Clear the Tablo Sync cache in Chrome and re-sync.
05). Now the Tablo should be stabilized and a good time to hook the USB drive back up and try another format.