I am using 300B as well. Never have your problem.
The only problems were;
1/ couldn't play some MKV files..only sound...but ok now after firmware update.
2/ Now, some files couldn't play for teh first time, but stop and wait for another couple sec, i.e.- 10 sec, try again and it will play.
Once the file played, it plays perfectly except there was corruptions in the file.