Why I got @error executing this code?

$nPORT = 8092
$IP1 = GetIP() ;IP Adress is correct too;
If $MainSocket = -1 Then
While $MainSocket = -1 Or $MainSocket = 0
$MainSocket = TCPListen($IP1, $nPORT)
If @error Then
MsgBox(0, "", $IP1 & " port"& $nPORT &)
$nPORT +=1
EndIf
WEnd
EndIf