I've just gone through a long incremental upgrade process from CiviCRM 4.2.19 to 4.7.25. Thought everything was working well until I discovered non-admin users were getting permission denied errors, so I tried to check the ACL settings -- and I can't access the Joomla Access Control settings.
When I go to "Administer->Users and Permissions->Permissions (Access Control)" and click "Joomla Access Control", the popup window shows
"500 - An error has occurred. JHtml: :bootstrap not supported. File not found."
Error logs aren't helpful -- nothing in PHP or CiviCRM logs, and Apache error just reports that the request for "/administrator/index.php?option=com_config&view=component&component=com_civicrm&tmpl=component" has returned a 500.
- Joomla 2.5.28 (yes I know it needs upgrading, that's happening as part of this whole site upgrade!)
- CiviCRM 4.7.25
- PHP 5.6