Upgrade to 5.6.6 to 5.8.17

We had a similar problem as to what was previously recorded in confluence here, but we cannot see the resolution. Just that a bug was resolved. Please advise.

Our errors are:
2016-07-05 20:15:23,871 ERROR [localhost-startStop-1] [atlassian.confluence.upgrade.UpgradeLauncherServletContextListener] contextInitialized Upgrade failed, application will not start: Upgrade task com.atlassian.confluence.upgrade.upgradetask.attachmentceo.AttachmentToCeoConversionUpgradeTask@19523a9 failed during the SCHEMA_UPGRADE phase due to: PreparedStatementCallback; SQL [insert into CONTENT(CONTENTID, CONTENTTYPE, TITLE, PAGEID, CREATOR, CREATIONDATE, LASTMODIFIER, LASTMODDATE, VERSIONCOMMENT, VERSION, PREVVER) select ATTACHMENTID, ? as CONTENTTYPE, TITLE, PAGEID, CREATOR, CREATIONDATE, LASTMODIFIER, LASTMODDATE, ATTACHMENT_COMMENT, ATTVERSION, PREVVER from ATTACHMENTS where ATTACHMENTID >= ? and ATTACHMENTID <= ?]; Cannot add or update a child row: a foreign key constraint fails (`databasename`.`CONTENT`, CONSTRAINT `FK6382C0598C38FBEA` FOREIGN KEY (`PAGEID`) REFERENCES `CONTENT` (`CONTENTID`)); nested exception is com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`databasename`.`CONTENT`, CONSTRAINT `FK6382C0598C38FBEA` FOREIGN KEY (`PAGEID`) REFERENCES `CONTENT` (`CONTENTID`))
2016-07-05 20:15:23,874 ERROR [localhost-startStop-1] [atlassian.confluence.upgrade.UpgradeLauncherServletContextListener] contextInitialized 1 errors were encountered during upgrade:
2016-07-05 20:15:23,874 ERROR [localhost-startStop-1] [atlassian.confluence.upgrade.UpgradeLauncherServletContextListener] contextInitialized 1: PreparedStatementCallback; SQL [insert into CONTENT(CONTENTID, CONTENTTYPE, TITLE, PAGEID, CREATOR, CREATIONDATE, LASTMODIFIER, LASTMODDATE, VERSIONCOMMENT, VERSION, PREVVER) select ATTACHMENTID, ? as CONTENTTYPE, TITLE, PAGEID, CREATOR, CREATIONDATE, LASTMODIFIER, LASTMODDATE, ATTACHMENT_COMMENT, ATTVERSION, PREVVER from ATTACHMENTS where ATTACHMENTID >= ? and ATTACHMENTID <= ?]; Cannot add or update a child row: a foreign key constraint fails (`databasename`.`CONTENT`, CONSTRAINT `FK6382C0598C38FBEA` FOREIGN KEY (`PAGEID`) REFERENCES `CONTENT` (`CONTENTID`)); nested exception is com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Cannot add or update a child row: a foreign key constraint fails (`confluencedb2016`.`CONTENT`, CONSTRAINT `FK6382C0598C38FBEA` FOREIGN KEY (`PAGEID`) REFERENCES `CONTENT` (`CONTENTID`))