1. add a blank aspx page to the root of the DNN 5.6.0 site
2. Navigate to the page in the browser (works fine)
3. Move the page to any subfolder
4. Navigate to the page in the browser (get a NullReferenceException - http://i51.tinypic.com/2ztk3o6.jpg) 

Thanks to Limno with his answer in another thread here: Try to add one entry in your PortalAlias table: yourPortaleID in PortalID column and your folder name in Portalalias column and leave other columns null. For example: INSERT INTO {databaseOwner}{objectQualifier}PortalAlias (PortalID, HTTPAlias) VALUES (0, 'www.yourdnnName.com/theFoldername') Restart your application after you add the record. this solved it for now! Any answers why this is happening would be good to know.