BradV is right, Although to keep the script more in the type of code you put it in, I'd put it like this:
 Code:
If InGroup("P_printer_###_***")
  If KeyExist("HKCU\Printers\Connections\,,AS-01,printer_###_***\")
    $=AddPrinterConnection("\\"+$ASERVER+"\printer_###_blanco")
    ? "printer_###_*** nieuw geinstalleerd"+"Error: "+@ERROR
  EndIf
Else
  If KeyExist("HKCU\Printers\Connections\,,AS-01,printer_###_***\")
    $=DelPrinterConnection("\\"+$ASERVER+"\printer_###_blanco")
    ? "printer_###_*** verwijderd"+"Error: "+@ERROR
  EndIf
EndIf