There has been a critical error processing your request

SQL Error: Deadlock found when trying to get lock; try restarting transaction\nError No: 1213\nSQL: DELETE FROM `shop_online_customers`
WHERE `date_added`< (NOW() - INTERVAL 1 HOUR)PHP call stack:
#0 /home/upnar99/public_html/marketplace/core/lib/db.php:138
#1 /home/upnar99/public_html/marketplace/core/engine/extensions.php:1175
#2 /home/upnar99/public_html/marketplace/core/engine/extensions.php:406
#3 /home/upnar99/public_html/marketplace/core/lib/db.php:104
#4 /home/upnar99/public_html/marketplace/storefront/model/tool/online_now.php:70
#5 /home/upnar99/public_html/marketplace/storefront/model/tool/online_now.php:39
#6 /home/upnar99/public_html/marketplace/core/lib/customer.php:158
#7 /home/upnar99/public_html/marketplace/index.php:66
in /home/upnar99/public_html/marketplace/core/database/amysqli.php on line 179