I have that issue with two players - Apacer and Noxxon, so I believe it is not because of them.
I use a home network and all my PCs and devices (including players ans the NAS) are in "workgroup" group.
So my players simply doesn't see the NAS as a SAMBA share if some of my PC's are not turned on. If they are there is no problem. But if I've forgotten to turn on a PC first I need to do it and in a 20-30 seconds the player starts to see the shares.
Any idea?