I had made a test after this update.
http://i.imgur.com/N3gYLCa.pngthe message under the indicator is Encode Failed - cause by another process is using the file 'C:\Users\EllisCheng\AppData\Local\Temp\folder.jpg', so it could not be accessed. It is file contention, but I don't have any idea what process would occupy that file, I had go to that directory once the error appears, there does not exist such a file named folder.jpg, I also checked for that path after the sync, still no folder.jpg there.
http://i.imgur.com/hohHSQT.pngThe first screenshot is the error message, though the song encode failed is not that one, the status had some problem when I scrolled up to that position, the file that failed to encode is BRIGHT STREAM.
The progress still stays as the second screenshot for a long time but will continue just like I mentioned before, no other encoding or volume leveling fail happened except that one.
http://i.imgur.com/UOBslPv.pngThis is the after all report, looks like musicbee will have a retry on the file which failed to encode, so BRIGHT STREAM appeared twice, and I had take a look under the path where it should be saved, it's perfectly converted and put to there.