Why "Internel error" in Redmine when exporting to PDF, if the task status is changed from "new" to any other?

Question

Redmine

In general, the whole point of the question is in the title, I ask for help.
Message text in browser: Internal error
An error occurred on the page you were trying to access.
If you continue to experience problems please contact your Redmine administrator for assistance.
If you are the Redmine administrator, check your log files for details about the error.