I think the default radiobuttons and checkboxes are part of the browser; if they are missing your browser may be corrupt.
The red X means the browser cannot find the images of 'check all that apply' etc.
Maybe you deleted a directory or moved the course but only a part of it?
Or maybe just some of the images are deleted?
I would rebuild the course, using the source you already made.
If the images are missing during preview, maybe the installation of CL is corrupt; reinstalling would add the missing images.