Fatal error: Call to undefined function: array_diff_key() — HELP!

Hello! Please help! I installed a new widget (a flash gallery, dont remember the exact name) and ever since I havent been able to log in to edit my website. the site is still up but it wont let me log in, i just keep getting this message:

Fatal error: Call to undefined function: array_diff_key() in /home/content/a/z/t/aztexpress/html/matthewziff/wp-content/plugins/flash-album-gallery/admin/admin.php on line 28

the site is my personal site: matthewziff.com

its hosted on a friend’s personal server but he is away so i have to wait till he gets back… until then, can anyone help me?

kthx!