Feedbuner seems to have problems even using hte format you have suggested in a prior post.
When its a wordpress site I can link to the wordpress feeds however it seems ot have problems with feedburner.
For example the followign two test samples do not work
[rssinpage rssdateformat='j M Y' rssdescription='no' rssitems='2' rsstarget='_blank' rssfeed= 'http://feeds.feedburner.com/FillTheFunnel?format=xml']
[rssinpage rssfeed= 'http://feeds.feedburner.com/SellingToBigCompaniesBlog?format=xml']
I used these two test items with other working wordpress based rssfeeds using the same pluging.