It looks like you did not follow Step 5 in the Install_Instructions.txt file which asks you to execute these SQL statements on your database:
ALTER TABLE customers ADD purchased_without_account TINYINT(1) UNSIGNED DEFAULT '0' NOT NULL AFTER customers_id;
ALTER TABLE customers ADD INDEX (purchased_without_account);
INSERT INTO configuration_group VALUES (40, 'Accounts', 'Configuration of Account settings', 40, 1);
INSERT INTO configuration VALUES ('', 'Purchase Without Account', 'PWA_ON','true','Allow Customers to purchase without an account', 40, 1, '2003-04-08 13:07:44', '2003-04-08 12:10:51', NULL, 'tep_cfg_select_option(array(\'true\', \'false\'),');
ALTER TABLE orders ADD purchased_without_account TINYINT (1) UNSIGNED DEFAULT '0' NOT NULL;
This is just a quick guess on my part!