I can confirm that this is an error only with the Ubuntu 15.04 package. Removing the Ubuntu package and installing the binary from the above link works for importing EPUB files.
** Also affects: calibre (Ubuntu) Importance: Undecided Status: New ** No longer affects: calibre (Ubuntu) -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1493627 Title: ePub files not adding to Calibre library Ubuntu 15.04 calibre, version 2.20.0 ERROR: Cannot add books: Failed to add some books, click "Show details" for more information. Worker process crashed while executing job : EOFError To manage notifications about this bug go to: https://bugs.launchpad.net/calibre/+bug/1493627/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs