ELGG 1.8 Embed plugin does not work at all


I've just installed ELGG 1.8 and with the defaut configuration + user dashborad and site-wide categories activated, embed plugin does not work at all :

If i click on embed in comment or blog post or wherever in site, it just display a blank frame with "No files" and updload a file display the same.

I try to search a solution in discussion and FAQ but no one seems to have this problems.

Could you help me ?