theme activation issues

Hi – It seems that I have successfully uploaded 2 different themes via FTP (as I see theme on my theme page), however when I click on Preview or try to Activate it, I get an error message:
Fatal error: Call to undefined function body_class() in /nas01/HostingVol1/49/42549/joeroma.com/nic_wordpress/wp-content/themes/oulipo/header.php on line 25

Any thoughts on how to activate? I assume that since it’s sitting in the Themes section, it has uploaded properly. Help! And thanks – Joe