[Zedder]

Thats because the syntax is wrong.You cannot format a string inside SendClientMessageToAll. You need to format the string first and you also forgot '[' after tempadminname.
here is the corrected code.

PHP код:

//You need to format the strings before putting it in SendClientMessageToAll.
new admnotification[128];
format(admnotification, sizeof(admnotification), "Administrator %s is now On-Duty!", playerData[playerid][tempAdminName]);
SendClientMessageToAll(COLOR_LIGHTBLUE, admnotification);