Ensure file download expiration times are reasonable to avoid database errors

I can't get my file downloads to assign to the user after purchase. I have just upgraded from Drupal 6 to drupal 7. the files do appear when i look at the 'order' but when you go to the user's 'files' page (user/*/purchased-files) it says 'No downloads found'. there is an option to manually add the files. when I use this to manually add the files the website throws up this error:

PDOException: SQLSTATE[22003]: Numeric value out of range: 1264 Out of range value for column 'expiration' at row 1: INSERT INTO {uc_file_users} (fid, uid, pfid, file_key, granted, expiration, accessed, addresses, download_limit, address_limit) VALUES (:db_insert_placeholder_0, :db_insert_placeholder_1, :db_insert_placeholder_2, :db_insert_placeholder_3, :db_insert_placeholder_4, :db_insert_placeholder_5, :db_insert_placeholder_6, :db_insert_placeholder_7, :db_insert_placeholder_8, :db_insert_placeholder_9); Array ( [:db_insert_placeholder_0] => 144 [:db_insert_placeholder_1] => 644 [:db_insert_placeholder_2] => [:db_insert_placeholder_3] => dPrqZzEB5XwhGOhReVL0zvY6X0Mdwk65o9C1q8Qp1AU [:db_insert_placeholder_4] => 1365500694 [:db_insert_placeholder_5] => 2943341094 [:db_insert_placeholder_6] => 0 [:db_insert_placeholder_7] => a:0:{} [:db_insert_placeholder_8] => 10 [:db_insert_placeholder_9] => 0 ) in drupal_write_record() (line 7106 of /home/sit
es/*.com/public_html/includes/common.inc).