My suggestion is to verify compatibility between the DLNA server and the bluray players. Format a basic 2/4/8/16GB thumbdrive, copy a few movies, pictures and music. Then connect it to the router and try. If it works then my guess is something with the files. Could be anything from way too many folders/sub folders or a file having a funny character in the filename. The thumbdrive test is basically to even see if the two will even talk.
Personally I am not a fan of UPNP-AV/DLNA. Even from day one I wondered why media players don't just use SMB/Samba. Finally WD Live and a few others including Boxee Box provides both UPNP/DLNA and Samba and there is a night and day difference in terms of ease of use and just "getting the movie to play!".
I checked a few of the new Panasonic models and they have "network drive access" on the spec sheet. If this is what I think it is, you'd be much better off using that instead. Like I said, if you can see the share on your network then you can forget DLNA completely. The overall performance is usually better as well.
Hope this helps