Unable to create subtask of issues

[Mrityunjay Kumar]

Hi Team

We are upgrading JIRA 5.2.1 to JIRA 6.4.2 and we are facing below error.

We are unable to create subtask of issues

Link of log file 

If any changes in DB is required for resolving this error please let me know how identify which DB is used and connect to it.

Thanks

[Phill Fox]

This looks similar to the problem answered in Duplicate LexoRank. Please review the response here, alternatively you may wish to contact Atlassian support and raise a support ticket to have their assistance in resolving this issue.