You need a try/catch around the propertyBag.Read, which throws an exception if the property does not exist. This is the expected behaviour when using the component at design time for the first time.
try
{
object value;
propertyBag.Read(“GnuPGEXE”, out value, 0);
if (value != null) strGnuPGEXE = (string)value;
}
catch (Exception)
{
strGnuPGEXE = null;
}