Here is a reproducer:

// NetAddr.broadcastFlag = true; 

n =  NetAddr("255.255.255.255", 57120);
n.sendMsg("/test");

Throws the following error:

caught exception in primitive NetAddr:sendMsg
ERROR: address_v4 from unsigned longERROR: Primitive '_NetAddr_SendMsg' failed.
Failed.
RECEIVER:
Instance of NetAddr { (0x1190785a8, gc=98, fmt=00, flg=00, set=02)
instance variables [4]
addr : Integer -1
port : Integer 57120
hostname : "255.255.255.255"
socket : nil
}
PATH: /Volumes/data/sc/(this)/__projekte/NetworkedAgain/Tasks networking.scd
CALL STACK:
MethodError:reportError 0x11b7b8498
arg this =
Nil:handleError 0x11b7b5738
arg this = nil
arg error =
Thread:handleError 0x11b704098
arg this =
arg error =
Object:throw 0x11b7b8ee8
arg this =
Object:primitiveFailed 0x11a13d648
arg this =
Interpreter:interpretPrintCmdLine 0x11a303048
arg this =
var res = nil
var func =
var code = "n.sendMsg("/test", \symbol);"
var doc =
var ideClass =
Process:interpretPrintCmdLine 0x11b7b6c88
arg this =
^^ The preceding error dump is for ERROR: Primitive '_NetAddr_SendMsg' failed.
Failed.
RECEIVER: a NetAddr(255.255.255.255, 57120)