SP Page builder not working on fronend, no preview either

Hi ! I have created 2 pages in SP Page builder and I wanted to preview these pages, but I get an error page when I do. I did not have this problem when I used this extension with another website 2 months ago. I then tried the frontend. They ask to enter password. But after, I do not see anything. For one page, I had downloaded a page template in the backend, and it does not show if I go on the frontend editor. If I go from the backend and use preview, this is what the page says : ""Object of class stdClass could not be converted to string"".
I prefer working on the backend and use preview.
But what is going on ?