Jetson TX2での開発を行っていたら、突然ホストPC側で「sudo apt-get update」
でのエラーが発生

Err:41 http://us.archive.ubuntu.com/ubuntu xenial/main arm64 Packages
404 Not Found [IP: 91.189.91.23 80]
Ign:52 http://us.archive.ubuntu.com/ubuntu xenial/universe arm64 Packages
Ign:58 http://us.archive.ubuntu.com/ubuntu xenial/multiverse arm64 Packages
Err:64 http://us.archive.ubuntu.com/ubuntu xenial-updates/main arm64 Packages
404 Not Found [IP: 91.189.91.23 80]
Ign:74 http://us.archive.ubuntu.com/ubuntu xenial-updates/universe arm64 Packages
Ign:80 http://us.archive.ubuntu.com/ubuntu xenial-updates/multiverse arm64 Packages
Err:86 http://us.archive.ubuntu.com/ubuntu xenial-backports/main arm64 Packages
404 Not Found [IP: 91.189.91.23 80]
Ign:93 http://us.archive.ubuntu.com/ubuntu xenial-backports/universe arm64 Packages
Fetched 553 kB in 3s (147 kB/s)
Reading package lists... Done
W: Invalid 'Date' entry in Release file /var/lib/apt/lists/_var_nv-deep-learning-repo-ga-cuda8.0-digits5.0_Release
E: Failed to fetch http://security.ubuntu.com/ubuntu/dists/xenial-security/main/binary-arm64/Packages 404 Not Found [IP: 91.189.91.23 80]
E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial/main/binary-arm64/Packages 404 Not Found [IP: 91.189.91.23 80]
E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial-updates/main/binary-arm64/Packages 404 Not Found [IP: 91.189.91.23 80]
E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial-backports/main/binary-arm64/Packages 404 Not Found [IP: 91.189.91.23 80]
E: Some index files failed to download. They have been ignored, or old ones used instead.

いろいろ試したけどだめだった。
行き着いた先が
NVIDIA DEVELOPER Ubuntu 14.04/16.04 and Jetpack 3.0

> sudo apt-get purge ".*:arm64"
...
> dpkg --remove-architecture arm64

以上のコマンドで無事「sudo apt-get update」ができるようになった。