Hi, PetraP
I am having the same problem here. The link seems to be the problem,, My situation is identical to hdepiano
One thing I did notice is that, on two other blogs of mine where the plugin is working, the “Sign In” button takes me to https://prefs.zemanta.com/UNIQUE CODE/?platform=wordpress39 while the same button on the site that isn’t working links to https://MY DOMAIN/wp-admin/post.php?platform=wordpress39
except in my case the sign in button also takes me back to my lists of posts.
And as with hdepiano, all of my other sites work fine. on this perticular site I have removed the plugin added it back in, have also removed my theme, and went back to the original, turned off other plugins etc.. can not seem to see why it is only happening on this one site.
Is there an override, for that link, exg. if I could find the unique code and build the url my self might that log me in?
Thanks,