An administrator created a new custom object.

Confirm the object is marked as deployed and not in development is what the administrator should do to resolve the issue. A custom object can be marked as deployed or in development depending on its readiness for use. A custom object that is marked as in development is not visible to users or available for data import or export. A custom object that is marked as deployed is visible to users and available for data import or export. Therefore, the administrator should make sure that the new custom object is marked as deployed before using Data Loader to upload records to it