Upgrade StorageNature (www.nature.com)
Haven't check more recent issues, but for the oldest issues Zotero fails to save the PDF, even though it is available on the page as a direct link. Example:
http://www.nature.com/nature/journal/v2/n30/abs/002066a0.html
http://www.nature.com/nature/journal/v2/n30/abs/002066a0.html
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