Hi Stellajo,
I'd like to let you know that the LR file previews really aren't working properly lately, but mostly this happens to files that were created using v2.0 -- roughly you may find that LR files uploaded starting from November of last year would have the same issue. Marialuisa (the author of the file in your screenshot) has also reported this issue before, and so we have already added this to our to-do list!
Unfortunately we'll need a bit more time to get this sorted out (along with the various bugs you may or may not have encountered here in the forum), but just to let you know, we're on it already