Why am I receiving and error with Marketpress installation using the Showcase theme?

Hello,

I just activated the Showcase theme. When I went to activate the Marketpress plug-in i was directed to an error page that reads: There was an issue determining where MarketPress is installed. Please reinstall. http://willieshairdepot.com/wp-admin/plugins.php?action=activate&plugin=marketpress-2%2Fmarketpress.php&_wpnonce=8003081995

I am not sure why I am receiving this error.

Please help,
Phe