On a Sharepoint2013 site, there are some excel files uploaded to the list attachments and document library. When user clicks the excel file, it prompts an error:
This workbook cannot be opened because it is not stored in a trusted location. To Create a trusted location, contact your system administrator.
I have checked the Trusted Location settings and the default is for the whole ShaprePoint server.
Opening Word docs will download the word document.
One workaround for this issue is to force Excel documents to be opened in a Client application.
Try deactivating and activating "Open documents in Client Applications by Default" site collection feature for a try.
You could also run the following PowerShell to set SPList.DefaultItemOpen property value to open list items attachments in client application.
$web = get-spweb http://<site>
$list = $web.Lists["list name"]
$list.DefaultItemOpen = [Microsoft.SharePoint.DefaultItemOpen]::PreferClient
$list.update()
