// INDENT YOUR CODE!!!

{ //what's  this bracket ?

    if(strcmp(cmdtext, "/say", true, 4)==0) 
    {
        if( ! IsPlayerAdmin(playerid)) // added the ! as you want if he is NOT admin
        {
            SendClientMessage(playerid, COLOUR_ADMIN,"You are Not Logged In as Admin");
	    return 1;
        }
        new string[256];
        format(string, 256, "Admin: %s");
	SendClientMessageToAll(COLOUR_ADMIN,string);
	return 1;
    }

} // what's this bracket?
} // and you see that this bracket goes nowhere...remove it