In the log messages of your feed you see the following error:
Discovered missing publication date in {X} items in your feed.
The feed item does not indicate the date it was published. In RSS for example, there is an element called pubDate which indicates the date when the item was created (published). RSS Graffiti relies on that date to distinguish between old and new items. Every time an item is posted on your wall, RSS Graffiti writes down the date it was created (published in your feed) and from then on, it looks only for items newer than that, to further publish on your wall. If the publication date is missing (not supplied by the feed), then RSS Graffiti has no other way of knowing if the item is new or not and whether it has already been published on your wall or not. As a result items without a publication date are not posted at all on your wall.
If you have control over your feed then you are probably able to fix this issue by adding the publication date field to the feed.
If you are not in control of your feed then you need to ask the system administrator or developer that is controling your feed to add the publication date element to the feed.
If you can't do either of the above then unfortunately your feed cannot be used with RSS Graffiti.