This is likely your problem. You are using a mapped drive name. Mapped drives don’t exist in system context, only in user login context and MCEBuddy runs as a system service in system context.
Search Path -> P:\DVR
Change your path to a network path like \\network\share and it should work fine with the credentials. Same for your destination folder.
See the Common issues page for details on this topic.
Also ensure that your NAS date time is matching the comouter date time. One user had noted that the date times didn’t match the authentication fails.