I finally solved the problem....it's not a VLC problem!!!
My NAS was set to not accept new dlna player, and since my iphone 5S is the last arrived....
I apologize for any inconvenient I could have caused
Thank you
I have tried with an other upnp service (an app upnp/dlna from iPad) and VLC works fine also on iPhone 5s (VLC sees the server and the folders). So it seems the problem is only between original Synology upnp/dlna application and iPhone 5s (VLC sees the NAS, but nothing else).
I use the standard app from synology (all updated).
Upnp works perfectly on Sony Bravia television, on samsung television year 2011, on samsung television 2012.
Vlc works fine on iPad 2, on iPhone 3GS, iPhone 4S, but still doesn't work on my iPhone 5S....
Version 2.2.2 is ok with iPad 2 and iPhone 3GS. Unfortunately doesn't work on iPhone 5S (I can see my disk station but when I open it there are no folder available).
I tried already to cancel the app and reinstall, but no changes....any good idea?