The error:
[ArgumentNullException: Value cannot be null.
Parameter name: value]
Argotic.Common.Guard.ArgumentNotNullOrEmptyString(String value, String name) +65
Argotic.Syndication.RssChannel.set_Title(String value) +22
indicates it is trying to use null or empty string for the channel and that is not allowed. This comes from the Module Title, ie the name of the Blog instance. You should make sure it is not an empty string.
Hope that helps,
Joe