[Leonatus]

Originally Posted by Doitsu

Are you getting the same plugin error message when you open one of your older MR epubs or are you only getting the error message for newer epubs?

It's only in the newer ones.

If you're only getting the error message for newer epubs, please copy and paste the complete <metadata>...</metadata> section.

Here is the metadata section:

<metadata xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:opf="http://www.idpf.org/2007/opf">
    <dc:language>de</dc:language>
    <dc:title>Ein Baum im Odenwald</dc:title>
    <dc:date opf:event="modification">2020-01-27</dc:date>
    <meta name="Sigil version" content="1.0.0" />
    <dc:identifier id="BookId" opf:scheme="UUID">urn:uuid:835bd7ec-3a04-43db-86f7-b83d6f72dc8f</dc:identifier>
    <meta name="cover" content="Cover.jpg" />
  </metadata>

If the newer epubs don't have the default Sigil folder structure (Text, Styles etc.), try selecting Tools > Restructure Epub to Sigil Norm (Werkzeuge > EPUB-Datei in Standard-Sigil-EPUB-Datei umwandeln), before running the plugin.

I tried this, but then, my formattings are at least partly removed (font assignments).