Getting UI error while accessing task

Question

Hi 
 while user trying to access the task was getting the UI error like below but i am accessing with service account i am not getting error like below checked the security of document and folder everything seems fine please suggest on this 
 Error 
 Error Evaluating UI Expression Expression evaluation error [evaluation ID = c9b13:9d17a] in rule 'dm_attachmentreviewsection' (called by rule 'dm_executiontaskfor') at function 'document' [line 27]: User Does Not Have Rights to Perform this Operation

Mike Schmitt · Answer

You might need to take a deeper dive into what you're trying to have "document()" do here. In my experience, that error is almost always seen when attempting to call it on a document ID that's freshly-uploaded into a File Upload Field on a form that has not been Submitted - and thus it's still sitting in the "appian-only back-end purgatory" space, instead of having been moved to the normal Appian Filesystem where it's available for general use. I suppose you might also get the same error in the case of a user having severe lack-of-permission, but you say you've already checked for that.

Mike Schmitt · Answer

What happens if you try to use the document() function on that document ID from a blank expression rule editor?