Flipbook Stopped Display

I got a problem on my webpage with 3D Flip Book plugin. Before it worked as it should. But during the weekend something happened. The plugin in WordPress dashboard works but when I go to see those PDF files on the webpage they are not there, but the code is inserted into the module.

I tried to make a new 3D book and insert the newly generated code into the module and still nothing.

What went wrong?

Regards.