LMS 7.9.0 not playing mp3 files

Hi,

hope someone can help me to point me into the right direction. I have the following setup:

* LMS 7.9.0 (updated yesterday, but same problem) installed on a debian server
* Client - Kodi Mediacenter based on Openelec with Squeezelite plugin (currently the only client)
* All music files are also stored at the debian server locally (using a raid5)

Everything is fine as long as a play flac files. When I try to play a mp3 file, nothing is played and LMS Log says:
Couldn't create command line for mp3 playback for........

The same mp3 file plays fine, when I use kodi for playback instead of squeezelite (which means playing the file through kodi without the involvement of LMS).

I tried to find answers on the net an this forum, but had no luck. Where should I start searching (which logs, etc.). Since I am rather new to LMS, I am not even sure, if this is a client or server problem. Are there any codecs missing, because of debian not providing it?

Thanks for your help,
Jobe