Try these solutions:
1. Ensure your chosen UPnP server software can serve the file type you are trying to access
Some servers do not serve FLAC for instance.
2. Make sure the files are non-DRM
The Network Player can only play non-DRM files. Files that have DRM controls cannot be played by the Network Player. Some servers may be able to authorise and de-crypt Microsoft PlaysForSure before then serving the content to the Network Player but this operation is not guaranteed as it is purely a function of the server.
3. If attempting to play 24-bit WAV or FLAC content note a wired Ethernet connection is normally required for reliable operation due to bandwidth considerations
4. Check that the Network Player can play back the file type you are trying to access
WMA, AAC, HE AAC, AAC+, MP3, OGG Vorbis, FLAC, WAV, ALAC, AIFF can currently be played.
5. Ensure your PC/NAS drive are connected to the same network as your Network Player.
Ensure you have followed the required steps for PC/NAS drive configuration with a Network Player.
You can find out more about this in the following FAQ.