I just noticed that UPnP playback for Roku clients has been broken in one of the recent builds. Yesterday I upgraded MC on my server (that installation I use only for UPnP) to 375. I don't know the exact previous build there, but if I remember correctly it was 358. Unfortunately I couldn't return to that build because the oldest available beta version is 363 which doesn't work too. Therefore I had to revert to the current release version (329) which works. With the newer builds I can browse the MC server with my two Roku soundbridges (European models from Pinnacle, Radio and HomeMusic) as always, but if I try to play a playlist or a file they show an error message.
In the newer MC versions I can browse and play files from another UPnP device, an Archos 605 Wifi. The MC server options are the default Roku settings. I've also tried several other combinations of the UPnP server options but couldn't find one that works. So far, I had used a Roku with MC for several months without problems.