How to fix Sitemap error Google webmaster

How do I fix this? rosebudtattoos.com

Warning: Class __PHP_Incomplete_Class has no unserializer in /home/content/p3pnexwpnas06_data01/24/2928724/html/wp-content/object-cache.php on line 520
https://rosebudtattoos.com/services-view/custom-tattoos/ 2016-05-21T21:44:33+00:00 weekly 0.6 https://rosebudtattoos.com/wp-content/uploads/2011/07/couple.jpg https://rosebudtattoos.com/services-view/banger-tattoos/ 2016-05-21T21:39:48+00:00 weekly 0.6 https://rosebudtattoos.com/wp-content/uploads/2011/07/banger-e1448922635212.jpg https://rosebudtattoos.com/services-view/american-traditional/ 2016-05-21T21:36:10+00:00 weekly 0.6 https://rosebudtattoos.com/wp-content/uploads/2011/07/hawk.jpg