This error message can occur if a Turnitin assignment submission point that has been copied from a previous version of the course is re-used. The Turnitin system is not able to find a location for the submission, as it has not been created in the copying process and does not exist.
This means that none of your students will have been able to submit work to this assignment, so it will be safe to delete the assignment submission point and create a new one.
To avoid this issue, we recommend not re-using Turnitin submission points. It is best to create new Turnitin assignments each time you need to set up a submission point.