Used Zen Cart since 2013, love it! Having some trouble upgrading from v 1.5.1 to 1.5.5.

Store page displays this text at the bottom
WARNING: An Error occurred, please refresh the page and try again.

Trying to access the admin area I don't even get an option to log in, I just get this
WARNING: An Error occurred, please refresh the page and try again.

The resulting debug file contents are
[25-Mar-2016 14:47:17 America/Chicago] PHP Fatal error: 1:Can't create/write to file '/backups/mysqltmp/#sql_23f5_0.MYI' (Errcode: 13) :: select banners_id, banners_title, banners_image, banners_html_text, banners_open_new_windows, banners_url
from banners
where status = 1 and ( banners_group = 'SideBox-Banners') order by rand() ==> (as called by) /home/fisherfo/public_html/communityofcelebration.com/store/includes/functions/banner.php on line 184 <== in /home/fisherfo/public_html/communityofcelebration.com/store/includes/classes/db/mysql/query_factory.php on line 167


PHP = 5.4.35
mysql = 5.5.46-cll