How to fix a "Failed to fetch binary-armhf/Packages" error during apt-get update?

You might install the armhf cross tools which add armhf as foreign architecture (your architecture maybe i386 or amd64). You can launch this command to verify:

dpkg --print-foreign-architectures

If the output includes armhf, you can simply remove it by running the command:

sudo dpkg --remove-architecture armhf

Finally, launch your sudo apt-get update again.

The offending line was from the x86 source list. Removing it eliminated the error. The following is the correct list for armf architecture.

deb http://ports.ubuntu.com/ubuntu-ports/ trusty main
deb-src http://ports.ubuntu.com/ubuntu-ports/ trusty main
deb http://ports.ubuntu.com/ubuntu-ports/ trusty-updates main
deb-src http://ports.ubuntu.com/ubuntu-ports/ trusty-updates main
deb http://ports.ubuntu.com/ubuntu-ports/ trusty-security main
deb-src http://ports.ubuntu.com/ubuntu-ports/ trusty-security main