If anyone out there also uses #Wallabag (free, open-source "read-it-later" software you can self-host) and gets the "Error occurred while saving article" message from an extension (despite it actually still working!), I have a solution (since I couldn't find one anywhere else):
Make sure your /path/to/wallabag/var/ directory has the correct owner (in my case, www-data), because mine didn't, and I somehow missed that line in the install docs (oops).
