UpdraftPlus version 1.9.4, release almost exactly a year ago (23rd April 2014), introduced an all-new back-end for Google Drive.
One of the reasons we did this, was because Google had previously announced that in April 2015, they would be shutting down one of their interfaces for programs to use Google Drive.
Google have now done what they said they would. Their old way of accessing Google Drive has now been permanently removed. If you are still using a version of UpdraftPlus from before 1.9.4 to use Google Drive, then you must update to be able to carry on doing so.
David Anderson (founder, lead developer, UpdraftPlus)