“Item does not exist. It may have been deleted by another user.”
Remove everything after the ID value in the url for the item, after and including the first dot. You can then use the view screen to delete the item.
http://blog.incworx.com/blog/sharepoint-developer-blog/let-me-tell-you-how-i-conquered-item-does-not-exist-it-may-have-been-deleted-by-another-user