Symptoms

Anonymous Forms and Views not allowing access to File attachment after it was uploaded but have not yet been saved into SmartObject.

Diagnoses

When you have an anonymous view with an attached file you are going to get an authentication error. Even if you have done the steps described in K2 documentation on File Attachment Control the behavior is still the same. This is becaue Considerations section of above mentioned document explains that configuration settings are available that allow users to upload and download files using an Anonymous Access Form.

This means thay you can either upload files to anonymous form or download those which already saved to SmartObject, but you can't open files which have been just attached but not yet saved.

Resolution

This behaviour is per the K2 core security design and this is expected behavior. Because file is not saved to SMO yet and we do not allow anonymous access to ISO storage where image resides until it is saved.