Comment 1 for bug 892264

In bzr-explorer 1.2.1 the explorer.py line 1272, in edit_file is:

    msg = gettext("Failed to edit '%(path)s' using '%(editor)s'.") % \
            {'path': path, 'editor': editor}
    info = gettext(
        "You may want to install the matching application or change the configured editor.")
> details = unicode(ex)
    self.show_error(gettext("Sorry"), msg, info, details)

So, this a knock-on failure trying to format an error report including localised messages from the OS, see the existing bug report for more. To resolve the root cause, check your editor setting.