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Without going too far into metadata, file format etc (as I don't know a lot about these) is it worth trying different profiles if a video won't play?
I have a Panasonic DMP BD77 and find neither the General profile and Panasonic BD profile will work on some files.
But if convert these with Handbrake they plays OK., but it would be nice to not need to do that.

You can't hurt anything trying different profiles. The DirecTV profile transcodes everything, while the Generic profile does nothing. Everything else has some level of transcoding. I rarely use the DLNA player in my Panasonic TV anymore, as it just isn't that great of an interface. I usually use a Roku player. Without knowing more about the videos that won't play (container and codecs) there isn't much more I can say.

This is the 'DirecTV HD-DVR' profile? Didn't seem to make any diffence.
They're mp4 videos, is that any help ? Yes the Panasonic Recorder is a bit flakey but its all we have!

MP4 is a container, and can contain different audio and video codecs. You can determine what is inside the container following the instructions in the link in my sig line.

That would be odd if it won't play with the DTV profile, unless you have some strange codec in there.