I got the same error. The temp solution is to download the previous version 6.4.1. Uninstall the newest plugin. Install 6.4.1 version, then you will get another error but don’t worry.. just go to settings and save your options. Then widget will show up on dashboard.
There will be info about upgrade (to the 6.4.2), you can upgrade to newest version, but don’t go to settings again and don’t use Save option. The previous settings stay saved and plugin works.
This is temp solution but widget / plugin works OK.
