Check to make sure lines 60-62 in your uc_credit.module look like this:
<?php
db_query("DELETE upc.* FROM {uc_orders} AS uo LEFT JOIN {uc_payment_credit} "
."AS upc ON uo.order_id = upc.order_id WHERE uo.modified <= %d AND "
."uo.order_status = '%s'", $time, uc_order_state_default('in_checkout'));
?>If not, it may be you were updating from a version prior to the directory structure changes and as such will need to remove duplicate directories from root that exist in the /payment and /shipping subdirectories.
Joined: 08/07/2007