[Plugin: NextGEN Gallery] Problem with Album Thumbnail

Greetings,

For some reason only one of my album thumbnails is not showing. See here: http://www.sezin.org/art-photography/ I have tried everything, including deleting the album and adding it again but still the problem remains. I find it strange because the other album thumbnails are working just fine.

Can anyone help me sort this out?

Thank you in advance,

Sezin

http://ww.wp.xz.cn/extend/plugins/nextgen-gallery/