What action should be taken if the error specifies a file identifier exists attached to another document?

Choosing to check for duplicate IDs in the import file is the most effective action when confronted with the issue of a file identifier already being attached to another document. This is because the primary source of the error is likely due to the presence of a file identifier used for multiple documents, which can lead to data conflicts and confusion.

By examining the import file for duplicate IDs, you can identify any instances where the same identifier is inadvertently being assigned to multiple documents. Correcting these duplications before attempting to import or attach files can prevent errors related to identifier conflicts and ensure that each document has a unique identifier. This step is crucial in maintaining data integrity and preventing complications when managing documents within the system.

The other actions, while they might address different aspects of document management, do not directly tackle the root cause of the error regarding the existing file identifier. Therefore, ensuring the uniqueness of identifiers in the import file stands out as the most pertinent and effective approach in this situation.