Hello Jeb,
Thanks for your post. Unfortunately, Structure is not compatible with JIRA 5.2.8 due to a bug introduced by Atlassian in this patch version. The bug may affect other plugins as well.
We are currently waiting for reaction from Atlassian. If you have your own Atlassian contact or an active support, please ask them about this problem or raise . a support ticket to push them a bit. The related bug record is
https://jira.atlassian.com/browse/JRA-32038
The latest supported version is JIRA 5.2.7. If this is a new instance, I hope you can downgrade (use export/import to keep data).
I apologize for the inconvenience caused.
Kind regards,
Igor