What did you use to convert?
If you used iTunes, some users have had problems with some more recent versions when trying to play the resulting files. I use dBpoweramp Reference version 13 to do this and have no trouble at all (around 10,000 files, including English, European and Chinese language tags). The trick with dBpoweramp is to run the optimiser after conversion so that the file is optimised for streaming.
Hope this helps.
Roku M1000, M1001, M2000, R1000, Roberts WM-201, Stream 83i