No header

portfolio slideshow no longer shows up in my plugins and none of the slideshows work:
http://themodelingagency.net/?p=915

the above page is one example. when i try to reinstall I get this message:
Destination folder already exists. /home2/anteproj/public_html/themodelingagency/wp-content/plugins/portfolio-slideshow/

Plugin install failed.

before it disappeared there was a message saying something about a missing header

help!

http://wordpress.org/extend/plugins/portfolio-slideshow/