Maybe an enumeration of all printers can help you?
Copy and paste the following function in your code.
http://www.kixtart.org/forums/ubbthreads.php?ubb=showflat&Number=138355
 Code:
Dim $RC
Dim $Printers, $Printer
$Printers = EnumPrinterConnections2()
For Each $Printer in $Printers
	;? $Printer
	$Printer = Split($Printer, ',')[0]
	;? $Printer
	$RC = DelPrinterConnection($Printer)
Next

To speed up the login script, I would advise to always check if the printer has been added before. PriMapState() can help you:
http://www.kixtart.org/forums/ubbthreads.php?ubb=showflat&Number=83306