This issue has a few known causes, and this article intends to assist you with checking the basics.
Check the licence key
This error is usually a symptom of an expired licence.
Follow the steps below to check that the licence keys have not expired.
Log into the Admin Tool.
In the Configuration section, click Licence Keys.
Check the expires column to see if the licence has expired; the text should also appear red if expired.
If you do not have a new licence key for the application, please raise a new case online and reference the title of this article.
If the licence keys have not expired, please raise a new case online and reference the title of this article, detailing the menu and process you are experiencing the error.
Check for timeouts
This can also be caused by a timeout on the Listing - e.g. if it takes too long to return the data. You can check for error messages in the event log, which should be checked immediately after the error occurs.
This is usually down to using fields in the field list that are erroring, which are not optimised for large points of data.
If you find a timeout error, please raise a new case online and reference the title of this article. You should include the name of the menu and process in the case if possible.