There were some things fixed in the blog feed validation for version 184.108.40.206 of mojoPortal. However for the feed to validate correctly you should make sure in blog settings under feed settings that you have specified a name and email address for the feed managing editor, and it is a good idea to choose at least the top level category from the itunes list of categories.
You will find that the feed for the blog on this site does validate. (actually it did not validate until I added the managing editor name and email which I did just now).
Hope that helps,