When running as non-administrator, the new set of File system Enumeration APIs cannot be used to recursively enumerate files or folders in a reliable way. This is because the system enumerators throw exceptions when they encounter an inaccessible folder. Instead of ignoring the exception and moving on, the enumeration methods halt processing on the exception. Please note that Microsoft is aware of this and working on a fix:

https://connect.microsoft.com/VisualStudio/feedback/details/512171/directory-enumeratedirectory-etc-unusable-due-to-frequent-unauthorizedaccessexceptions-even-runas-administrator?wa=wsignin1.0