Turnitin introduced a change in Summer 2021 as to how the expiry of classes are managed (previously it was managed by the latest Turnitin ‘Post date’ in the module, now it is managed by the ‘Course end date’ in the Course settings).
When attempting to mark a Turnitin assignment for which the class is deemed to have “expired”, you will be presented with the message: “Read Only: This paper was submitted to a class that is expired, and is currently in read-only mode” (as shown in the screenshot below):

Follow the steps below to resolve the problem:
- From the course homepage, click the Settings ‘gear’ icon (on the right-hand side) and select Edit settings.
- Change the ‘Course end date’ to a date in the future (after which you don’t expect to need to change anything). Don’t extend it by any further than one year.

- Scroll down and click Save and display.
- Locate the Turnitin assignment on the course home page, and click Edit > Edit settings to visit the ‘Settings’ page for the dropbox.
- Don’t make any changes to the settings, simply scroll to the bottom of the page and click on Save and display – this is to effectively “wake it up” so that Turnitin will then check the ‘Course end date’ to ascertain whether the dropbox should be read-only or not.
You should now be able to add comments and grades to submissions in that dropbox.