The error has occurred as a side-effect of installing the A2DP Bluetooth streaming package.
You need to run the following:
sudo rm /etc/apt/sources.list.d/a2dp.list
Then follow the instructions here: Udisks.service fails after latest update - #25 by dillthedog to try to restore your system to its correct state.
Once you have followed the instructions, please run
sudo apt-get update
sudo apt-get dist-upgrade