Hi Jagi, sorry about the late reply.
Can you kindly tell me which lessons/words have this problem? If there are too many, you may simply list down a few of them so we can check. I would also like to know if you can preview the sound files from the Advanced Play/Edit screen (without playing the lesson) -- are the sound files playing fine in the preview, but not during the lesson, or does it look like there are actually no sound files for certain words?
In the meantime, please try using the Audio Diagnostic Tool and see if it helps. You may find detailed instructions on how to use this tool here:
How to use the Audio Diagnostic Tool
http://support.brillkids.com/index.php/article/ls-how-to-use-audio-diagnostic-toolIf the problem does not get fixed after using the tool, please let us know and attach a new Diagnostic Report so we may continue troubleshooting.