Service portal error "You are either not authorized or record is not valid." Another symptom is that the item will not be returned when searching for it. For issues with this same error in SP but for record producers. The user criteria may fail from the user criteria diagnostic tool when the conditions should pass.
The page contains the "SC Catalog Item" widget without a catalog item sys_id in the URL parameters.
There is a User Criteria applied to the Item you are trying to open which prevents the user from accessing it.
A field on the record producer named "Hide on service portal" which will not allow the user to see the record producer in the Service Portal and users will see this same error.
Remove the SC Catalog Item widget from the page if not needed. Make sure that a "&sys_id=" parameter is present in the URL with a value of a sys_id for a catalog item.
Review User Criteria on the item to make sure they have the right access. The User Criteria Diagnostic module can be used for this.
Check the "Hide on service portal" field on record producer to false.