[xwiki-devs] XWiki 6.3 Flamingo disappeared after import large XAR

I have installed XWiki enterprise 6.3 Flamingo skin is visibile. After import my previous XWiki 5.1 content, using extension Large+XAR+Import, Flamingo skin disappeared. XWiki is exactly 5.1 style and I can't select Flamingo from Admin panel. Why ? Ho to restore Flamingo ? Andrea