Debugging Cron get "Duplicate entry '' for key 'uc_guid'

Every newsletter that tries to send I get this error below, using Version 5.6.7

WordPress database error Duplicate entry ” for key ‘uc_guid’ for query INSERT INTO wp99_posts (post_author, post_date, post_date_gmt, post_content, post_content_filtered, post_title, post_excerpt, post_status, post_type, comment_status, ping_status, post_password, post_name, to_ping, pinged, post_modified, post_modified_gmt, post_parent, menu_order, post_mime_type, guid) VALUES (0, ‘2018-09-11 10:23:02’, ‘2018-09-11 16:23:02’, ‘\r\n\r\n\r\n<title>Newsletter</title>\r\n\r\n\r\n\r\n/* CLIENT-SPECIFIC STYLES */\r\n#outlook a{padding:0;} /* Force Outlook to provide a \”view in browser\” message */\r\n.ReadMsgBody{width:100%;} .ExternalClass{width:100%;} /* Force Hotmail to display emails at full width */\r\n.ExternalClass, .ExternalClass p, .ExternalClass span, .ExternalClass font, .ExternalClass td, .ExternalClass div {line-height: 100%;} /* Force Hotmail to display normal line spacing */\r\nbody, table, td, a{-webkit-text-size-adjust:100%; -ms-text-size-adjust:100%;} /* Prevent WebKit and Windows mobile changing default text sizes */\r\ntable, td{mso-table-lspace:0pt; mso-table-rspace:0pt;} /* Remove spacing between tables in Outlook 2007 and up */\r\nimg{-ms-interpolation-mode:bicubic;} /* Allow smoother rendering of resized image in Internet Explorer */\r\n\r\n/* RESET STYLES */\r\nbody{margin:0; padding:0; height:100% !important; margin:0; padding:0; width:100% !important;}\r\nimg{border:0; height:auto; line-height:100%; outline:none; text-decoration:none;}\r\ntable{border-collapse:collapse !important;}\r\n\r\n\r\n/* MOBILE STYLES */\r\n@media screen and (max-width: 525px) {\r\n\r\n /* ALLOWS FOR FLUID TABLES */\r\n table[class=\”wrapper\”]{\r\n width:100% !important;\r\n }\r\n\r\n /* ADJUSTS LAYOUT OF LOGO IMAGE */\r\n td[class=\”logo\”]{\r\n text-align: left;\r\n padding: 20px 0 20px 0 !important;\r\n }\r\n\r\n td[class=\”logo\”] img{\r\n margin:0 auto!important;\r\n }\r\n\r\n /* USE THESE CLASSES TO HIDE CONTENT ON MOBILE */\r\n td[class=\”mobile-hide\”]{\r\n display:none;}\r\n\r\n img[class=\”mobile-hide\”]{\r\n display: none !important;\r\n }\r\n\r\n img[class=\”img-max\”]{\r\n max-width: 100% !important;\r\n width: 100% !important;\r\n height:auto !important;\r\n }\r\n\r\n /* FULL-WIDTH TABLES */\r\n table[class=\”responsive-table\”]{\r\n width:100%!important;\r\n }\r\n\r\n /* UTILITY CLASSES FOR ADJUSTING PADDING ON MOBILE */\r\n td[class=\”padding\”]{\r\n padding: 10px 5% 15px 5% !important;\r\n }\r\n\r\n td[class=\”padding-copy\”]{\r\n padding: 10px 5% 10px 5% t=\”\”

*****DELETED MOST OF CONTENT TO SHORTEN

src=\”http://www.mydomain.com/?noti=MTszNDA7NmJiMzQzNTliZDgzYjg3NjM5YjU5ZWI3MTFiNjUzYzA%3D\” />\r\n’, ”, ‘Selling Your Home? Get 1% Back at Closing if you Buy & Sell with Me’, ”, ‘private’, ‘postman_sent_mail’, ‘closed’, ‘closed’, ”, ‘selling-your-home-get-1-back-at-closing-if-you-buy-sell-with-me’, ”, ”, ‘2018-09-11 10:23:52’, ‘2018-09-11 16:23:52’, 0, 0, ”, ”) made by do_action_ref_array, WP_Hook->do_action, WP_Hook->apply_filters, Newsletter->hook_newsletter, Newsletter->send, Newsletter->mail, wp_mail, PostmanWpMail->send, PostmanWpMail->sendMessage, PostmanEmailLogService->writeSuccessLog, PostmanEmailLogService->writeToEmailLog, wp_insert_post