friends-app crashes on start

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http://askubuntu.com – Whenever I try and start friends-app, it crashes with the error: friends-dispatcher crashed with ValueError in raw_decode(): No JSON object could be decoded I've tried reinstalling but that didn't help. It works fine on another PC (logging in to the same Twitter account), also on 13.04. The apport error lists the crash as a duplicate of https://bugs.launchpad.net/bugs/1166432, but that just 404s, so I don't know what the underlying issue is. How do I fix the problem? (HowTos)