How can I diagnose publish failing to store result?

We are using Knowledge Center. A publish succeeds running DITA-OT but then fails when storing the result:

Unable to store the result. See eventdata for more details.

The evendata says:

ExportDataToFileSystem started - lTotalNoOfLngCardIds99

ExportDataToFileSystem started

ExportDataToFileSystem started - lTotalNoOfLngCardIds3166

Unable to store the result

 

Do you know what could be causing this?