Software & Updates crashes and will not open

I had the same issue, Ubuntu 16.04, 64-bit and a reinstall of all the supporting packages:

sudo aptitude reinstall apt apt-utils aptdaemon aptdaemon-data update-manager update-manager-core dbus

solved the issue. For note, a temporary workaround was to run sudo aptd in another terminal before running update-manager, and then update-manager was able to connect to aptd over dbus.

Unfortunately, I can't determine which package was the precise fix now that my issue is solved but if you try reinstalling each one-by-one, you can report back. A number of packages are/were broken on my system by a failed install resulting in odd issues like this one because of missing files, permissions and scripts; reinstalling packages is fixing these problems.

I was about to reinstall the system until I found davidjb's solution.

So,

sudo apt-get install aptitude

followed by

sudo aptitude reinstall dbus

solved this problem for me.

to add my 2 cents: Ubuntu-Mate 16.04, installed 15-June-2017, all updates. Similar problem appeared (dbus.exceptions.DBusExcept etc), solved by:

sudo aptitude reinstall python-pkg-resources python3-pkg-resources

Cheers, Valentin