[Sascha]

what he said and in addition you should check whether the player who's name you want to change is actually connected (IsPlayerConnected) and you used "GetPlayerName(playerid,....)" whereas it should be "GetPlayerName(targetid,...)" as you want to have the name of the player you selected and not your own
so it would've changed your own name in the database and not the name of the player you selected :P