[Ripplinger]

I don't use that plugin myself (I much prefer standard epubs). But in the meantime until someone else familiar with the plugin reads this, I would first delete the book from the Aura, and then resend it to the Aura in the usual way. If the plugin still gives an error, try swapping the plugin back to the standard one that came with Calibre and delete the book and resend it again to see if it still gives an error.

It's been awhile I had to delete and resend a book, but if I remember correctly, I think it was suggested you disconnect the reader after deletion, let it index, and then reconnect it again to resend the same book to the device.

The results of this might be helpful to pinpoint where the issue is coming from for others to help out.

Edit: Another thing to try is to change what you have entered in the Title area for the series index. As an example, this is how mine reads:
{title} {series_index:|[|]} {series}

Possibly Kobo readers don't like the {series_index:05.2f}. Try using only what I have for the series_index and see if the error is still there.