Symptoms

Access denied error on the K2 smartform (OOTB display/edit/view forms) We have the requirement, the user is able to add new item and view an item in a list, but the user won't be able to access to the site. I have granted the user as "Add only & View only" permission to the list and "Restricted Interfaces for Translation" on the site level. It works for a out of box list form, but it doesn't work for K2 form.
 

Diagnoses

On this lockdown of rights, the users have no rights to the site but he is granted rights on the list where they need to work. This is all good, if K2Pages is used for the New/Edit/Display forms then you also need access to the location of that forms to read them.
 

Resolution

This is expected as the user cannot access the K2pages Library which is hidden due to the permissions given to the list directly and nothing on the site level. Navigate to SITEURL/K2pages this is the pages K2 needs to access as the user logged in, grant read rights to this library. NOTE: no changes should be made to the files in this library any changes to them will not be supported.