Omeka site will not come up

I am having a problem with the omeka part of my website, corenyc.org/omeka
corenyc.org/omeka/items

I am getting an error message -

Fatal error: Class 'Omeka_Application' not found in /home/ej7/corenyc.org/omeka/index.php on line 14

What do I need to do to fix this?

Omeka_Application is one of the core files for Omeka (at least for older versions of Omeka). It would normally be located at application/libraries/Omeka/Application.php. Do you have a file there?