title: Failure sending mail: An error has occurred during report processing.Mail will not be resent
body: <p>An SSRS email subscription did not work this morning. The error message I saw is &quot;Failure sending mail: An error has occurred during report processing.Mail will not be resent.&quot; When I checked the log files, I found out that there is an error in more than one dataset in the report. The report is reading data from Sharepoint. Please find below the error from the log file.</p>
  <blockquote>
  <p>Query execution failed for dataset 'WORK_PACKS'. ---&gt; &gt;System.ArgumentException: An item with the same key has already been added.</p>
  </blockquote>
  <blockquote>
  <p><em>ERROR:
  Throwing
  Microsoft.ReportingServices.ReportProcessing.ProcessingAbortedException:
  ,
  Microsoft.ReportingServices.ReportProcessing.ProcessingAbortedException:
  An error has occurred during report processing. ---&gt;
  Microsoft.ReportingServices.ReportProcessing.ReportProcessingException:
  Query execution failed for dataset 'CONSTRUCTION_ACTIVITIES'. ---&gt;
  System.ArgumentException: An item with the same key has already been
  added.</em></p>
  </blockquote>