Have you recently updated your Ubercart version?

Also, a little unrelated but do you know if they sell oat or corn flour?

I just checked all the logs, and found one Visitor error that happened twice:

Message You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '= '1') )' at line 1 query: SELECT count( DISTINCT(node.nid)) FROM node node INNER JOIN node_access na ON na.nid = node.nid WHERE (na.grant_view >= 1 AND ((na.gid = 0 AND na.realm = 'all') OR (na.gid = 1 AND na.realm = 'term_access'))) AND ( (node.status = '1') AND (.is_product = '1') ) in /usr/local/www/drupal-5.2/includes/database.mysql.inc on line 172.

On Update.php:

* user warning: Unknown column 'notify' in 'uc_order_statuses' query: ALTER TABLE uc_order_statuses CHANGE notify state VARCHAR(32) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL default '' in /usr/local/www/drupal-5.2/includes/database.mysql.inc on line 172.
* user warning: Duplicate column name 'weight' query: ALTER TABLE uc_order_statuses ADD weight MEDIUMINT(9) NOT NULL in /usr/local/www/drupal-5.2/includes/database.mysql.inc on line 172.
* user warning: Duplicate column name 'locked' query: ALTER TABLE uc_order_statuses ADD locked TINYINT NOT NULL DEFAULT '0' in /usr/local/www/drupal-5.2/includes/database.mysql.inc on line 172.

* ALTER TABLE {uc_order_statuses} CHANGE order_status_id order_status_id VARCHAR(32) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL default ''
* ALTER TABLE {uc_order_statuses} CHANGE title title VARCHAR(48) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL default ''
* Failed: ALTER TABLE {uc_order_statuses} CHANGE notify state VARCHAR(32) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL default ''
* Failed: ALTER TABLE {uc_order_statuses} ADD weight MEDIUMINT(9) NOT NULL
* Failed: ALTER TABLE {uc_order_statuses} ADD locked TINYINT NOT NULL DEFAULT '0'
* DELETE FROM {uc_order_statuses} WHERE order_status_id LIKE '_'
* INSERT INTO {uc_order_statuses} (order_status_id, title, state, weight, locked) VALUES ('payment_received', 'Payment received', 'payment_received', 10, 1);

Very weird... I don't think core really nailed down issues regarding dependencies in Drupal 5. Hopefully Drupal 6 fixes 'em!