Does my licence include the SEO Manager (Proffesional search optimization tool at your disposal. The missing OpenCart SEO functionality built right into the theme. A worthy rival of the existing premium extensions.)?
It seems there is a conflict with another extension of yours, but can’t recognize it from the screenshots you have attached. It may contain ‘seller’ in its name, judging by the source code. Can you try to deactivate it to see if the error message continue to appear ?