Long shot.
The disc your friend burned - was it set to a specific region? Perhaps your tricky readers don't like region free discs.
If you can - get a copy of a burn log from your friend.
Unfortunately I can't. Anyway, my standalone player reads single-layer DVDs burned the same way.
I've tried to burn 2,4x, 4x, 8x and 10x.
Edit: One copy burned at 8x was (by chance?) readable by the standalone. This proves that it reads region-free disks.
Most probably I have to clean both Matsushita combo and the standalone player, but I really wonder why it reads the same content burned by NEC but not by mine Pioneer that is supposed to be a good burner