I've been investigating an issue recently where the system/farm account received Native Code HRESULT Access Denied exceptions from SPRequest trying to access several folders in a large list.
Deep analysis shows that there are about 200 thousand items separated in folders according to recommendations and there are about 670 unique permissions in the site collection and 6 (six) SPFolders have NULL Permisions assigned according to the TVF used there (by ScopeId).
[Update] 500 INTERNAL SERVER ERROR is rendered when browsing to these folders [/Update]
The 6 SPFolders appear to have NO permissions assigned: looked into a copy of content DB table Perms and view Docs where left-joining by ScopeId gives NULL on the Perms side. Actually there are matches in Perms where Perms.ScopeUrl = Docs.DirName+'/'+Docs.LeafName but ScopeIds differ.
How should I get on with it?