The file store.auth is required to install and run your store.

This file does not come with the zipped up install package but
should have been provided separately by your vendor, perhaps via ftp.

If this is a reinstallation, copy the file named <store-id>.auth
from your data directory to the installation directory and name
it store.auth.

If this does not work, contact the vendor who sold you this
ShopSite software in order to obtain a valid auth file.