Are you using Internet Explorer by any chance? I've just noticed recently that I can't get any bumps to load in IE8... and I just checked and I also get that same "unavailable" message. I don't normally use IE so I don't know how long it's been going on.
...hmmm... scratch that, it may be entirely unrelated. I just opened Opera and none of the thumbnails were working.
I guess I better go check some others
... I can't fix any of it myself, though, so that sucks.
Yep, also not working in Firefox, Chrome & Safari.
Side note: the bump player loads fine in IE9, just not in IE8... I don't think I have any machines running any older versions.