For entities you can use enet_clent_create()/enet_svent_create(). It generates a global pointer that can be used on all participants. For more details, read the manual section regarding entity functions.
Why don't you use enet_set_playername() for managing the player name?
To say it in general: All pointers that are generated by Lite-C are invalid on a different participant!
Thank you! Got all to work now

And to your question why I dont use the anet func for playernames:
Because in the playerdisconnect event (which I use as timed out event) the client isnt valid anymore, but I need to say who timed out.