The @@hidden"code" is telling endnote to only list the citation in the bibliography and ignore it as a citation. You can view the temporay citation by selecting all and "converting citations to termprary (unformatted) citation which will look like this
{Mitelman, 1995 #1@@hidden} – and you could just search and replace @@hidden} for } to get rid of them all. Not sure how they got there though?