Vasilis, I’m guessing you pulled your post before anyone answered. If you use a web window instead of an HTML extension for the wordsearch it works fine. I think putting an iframe in a div is what is causing the problem. The content is trying to be styled before it is loaded and throws an error.
I could also place the image above the html extension, by layering the image above the html extension the normal way AND checking “Always on top” for the image. Maybe there’s a z-index conflict with objects on the external page or similar. As far as I can remember from playing around with jQuery mobile (but I’m not exactly sure), the library seems to influence several CSS properties of Lectora objects as well.