This issue can be caused when files with illegal characters in the file name are uploaded to a discussion topic. There is a workaround available.

  1. In the Discussions tool, click Settings.
  2. In the Default view section under Personal Settings, check if you are currently using Reading View. If so, select Grid View. Click Save.
  3. Return to the list of discussion topics and see if the error can be reproduced. 

If you are still unable to access the topic contact the Help Desk for further investigation.