When upgrading Jira from 6.x to 7.x it requires to upgrade The Scheduler from versions 3.x to 5.x. You might experience a 404 Error on Access Manager and stack trace on Statistics page.
The reason of the problem:
In newest version of TSP we had to remove one constraint from database. Your stack trace shows that for some reason this constraint was not removed from your database.
To resolve this issue you should run SQL query manually:
This will remove deprecated constraint - this should do the trick. Please notice that the DB schema could be other - the "jiradbschema" is default schema. Before firing queries, please make sure that the schema is like in your base.
Make this operations while plugin is disabled and make sure to re-enable it when it is done.
Related issues:
https://bitbucket.org/apdc/the-scheduler/issues/129/the-scheduler-can-not-access-accessa
https://bitbucket.org/apdc/the-scheduler/issues/201/the-scheduler-not-working-after-upgrade