i have had similar issues with trying to stream hd camcorder videos streaming to a ps3 and here are my workarounds:
the dns-323 firmware 1.07 does not recognize mts as a vaild a/v format. the uPnP only serves formats it recognizes, such as mp4.
to solve this,
1. i copied the folder and renamed the .mts files to .mp4. this should not change the file contents, and i'm assuming that since the uPnP AV server recognizes .mp4, it serves the .mts file over to the PS3. the file probably contains header information telling the client what the file is. i played it safe, that's why i made backup of the original files.
2. log into the dns box, and go to advanced > uPnp A/V Server > Refresh
3. Turn on PS3.