There are two possible causes for this. In this order, do the following checks:

  1. Click on one of the other 'purple' buttons under Preview, Save, or Download (e.g., Quick Save, Save and Preview Formatted) and look for a system response to your click (e.g., 'Document Saved!' popup; display of a formatted metadata record). If nothing appears in response to your click, this means that your logged in OME session has terminated, and you are no longer connected to the OME server; as a result, OME doesn't know that you are trying to Download Metadata Package. Return to the OME login page, login again, open your record, and then attempt to Download Metadata Package; validation will commence, and, if successful, your metadata zip file will download.
  2. The Metadata Parser (MP) service, which OME connects to in order to perform the validation and generate your metadata zip file, may be down. If you have eliminated #1 as a cause of Download Metadata Package failure, please submit a ticket to the OME Support Desk. MP is managed outside of the Science Analytics and Synthesis (SAS) program, but we will work with the owner of the tool to restore OME's access to the service as quickly as possible.