Thanks Aelfred, I ran into this error recently during a new install after my crappy laptop gave up the blue smoke ghost and had to reinstall on an even crappier laptop.

Delete the default.conf
Code:
sudo rm -f /usr/lib/x86_64-linux-gnu/qt-default/qtchooser/default.conf
then recreate the default.conf by typing

Code:
sudo xed /usr/lib/x86_64-linux-gnu/qt-default/qtchooser/default.conf
and add in the line from the instructions above and save the default.conf.