First one is to replace the following code:

If SetDefaultPrinter ("Periwinkle") = 0
? "Set default printer to Periwinkle..."
EndIf

with:

If SetDefaultPrinter("\\Charon\Periwinkle")=0
? "Set Default to \\Charon\Periwinkle printer"
ENDIF

or try this:

IF InGroup("Group")
$t= SetDefaultPrinter("\\Charon\Periwinkle")
? "Set default to \\Charon\Periwinkle"
ENDIF

Hope this will help you out!