Have been meaning to post this for a while.
I'm using a BDP-S370 running the latest firmware via a wired connection. I am using Serviio 0.5.2 on my PC (Core i7 920 @ 2.8GHz, 6GB RAM) and the actual video streams very well. I use the standard Sony Blu-Ray Player profile. Streaming m2ts or mkv (with transcoding on) freezes almost always at about 47-49 minutes, but as the others have said, can happen anywhere up to 90 minutes. The stream stops and dims, the 'connection to server lost' or similar message pops up, and I can hit stop then start and it will resume (almost) where it left off, most of the time. After that, there are no more dropouts or problems at all (even with Ben Hur!)
I have tried with a range of 1080p MT2S and MKV files of differing bitrates, encoding profiles and sound quality/bitrates, every concievable setting in serviio regarding transcoding and audio downmixing and so on, and still experience the problem. I have plenty of space on my hard disk drives and I have fiddled about with the temp folder as well. I've tried Serviio on each of my four physical hard drives in case it was to do with drive speed, and have had the serviio temp folders on the same drive as the installation, different drives, everything I can think of. I have closed all other running programs and have not noticed it make a difference.
The only possible thing I considered was maybe this was because I had a 64-bit version of windows 7 running, but I haven't reinstalled a 32-bit version just to test this as that would be a fairly major job. The other posters didn't state which edition of windows they were running so I can't work out whether that fits the pattern or not.
Hope we can get this thing sorted, it's annoying as hell (although it does provide a good excuse for a toilet break

)