Hi,
Verry sorry for the late response, I was working on the next release on this plugin.
I believe those error messages are related to a known problem, where the plugin tries to add itself to the end of the content, but in some cases it’s not correctly recognized.
I’m attaching a pre-release of the 1.6 version to this post. To update, please de-activate an delete the current one via the plugin manager, and install this one instead. All your configuration should remain in the database.
Make sure to have a site back-up before installing any plugin, just in case.
This release should fix the error message issue, and I have also fixed the WPML string translations.