Hash entry sometime is $NULL (error), and sometimes isn't? - powershell

Question

I have my little 3-sided socket-server. Each server has its own hash with its key-values.
The very first is:
$Local = #{ID="Local"; ...}
$RemtA = #{ID="RemtA"; ...}
$RemtB = #{ID="RemtB"; ...}
I start for all of the the listeners - no problem.
If now a client wants to connect, I want to add the ID to $ProgressHead, which is defined like this:
$ProgressHead = "Value-Broadcast, Connected: "
and used in my function to accept a client called with its hash as $h:
if ( !$h.Connected ) {
#Write-Host "$($h.ID) not connected, pending: $($h.listener.Pending())"
if ( $h.listener.Pending()) {
$h.client = $h.listener.AcceptTcpClient() # will block here until connection
$h.stream = $h.client.GetStream();
$h.writer = New-Object System.IO.StreamWriter $h.stream
$h.writer.AutoFlush = $true
$h.Connected = $true
Write-Host $Global:ProgressHead # fails - empty ??
Write-Host $h.ID # prints oh depit it is marked as error
if ( !$Global:ProgressHead.Contains( $h.ID ) ) { # <= HERE IS THE ERROR ????
$Global:ProgressHead= "$($Global:ProgressHead)$($h.ID) "
}
}
}
The Error message says:
Can't call a method for an expression which is NULL and $h.ID is underlined
BUT I DO NOT get any error if I start this either in the cmd-console when running powershell -file ThreeServer.ps1 or within the ISE in debug mode. The ID is written correctly to $ProgressHead!
Only if I start this in the Powershell console (PS C:\...> ./ThreeServer.ps1) I get this error, but all the other keys in the lines above are valid ONLY $h.ID on ONLY the PS-console throws this error?