It's possible that the server does not deliver those formats correctly (the TV may be expecting to see certain tags which that server is not providing) or the files themselves have codecs in them that cannot be played by the TV (even if the format is correct, the codecs inside are what really matters).
I am an author of another DLNA server that you may want to try - it's called KooRaRoo Media and it's available at http://www.kooraroo.com. I'd be happy to provide any assistance with it in case you find any issues, but I'm quite sure that it'll just work If you give it a try, please let me know what you think and how it goes. It's still very new (just a few weeks on the market) and there are many things planned for it. (end of self-promotion )
Dennis. Developer of KooRaRoo Media - the newest DLNA server on the market. Give it a try today by visiting http://www.kooraroo.com. Happy to assist with questions related to DLNA in general or KooRaRoo specifically.
Yeah Panasonic suck quite a bit when it comes to the DLNA media player, your model doesn't support the MPEG-4 ASP video format or the avi container.
All it supports is H.264/MKV or H.264/MP4 videos along with MPEG-1, MPEG-2 and AVCHD stuff.
If your box running FreeNAS has as good enough CPU it should be able to transcode the media in real time making it play but you need a DLNA server running on it that is capable of transcoding. Once such server is Serviio which can be installed on FreeNAS with some work.