Index: lams_gradebook/src/java/org/lamsfoundation/lams/gradebook/service/GradebookService.java
===================================================================
diff -u -r679782834f99e7e2699f9f34ae8bf1c75abc7bb5 -r26f41e753302e333a9566ed136f781f9ae207726
--- lams_gradebook/src/java/org/lamsfoundation/lams/gradebook/service/GradebookService.java	(.../GradebookService.java)	(revision 679782834f99e7e2699f9f34ae8bf1c75abc7bb5)
+++ lams_gradebook/src/java/org/lamsfoundation/lams/gradebook/service/GradebookService.java	(.../GradebookService.java)	(revision 26f41e753302e333a9566ed136f781f9ae207726)
@@ -1443,8 +1443,8 @@
 			Date finishDate = getActivityFinishDate(learnerProgress, activity, null);
 			activityDataRow[2] = new ExcelCell(finishDate == null ? ""
 				: FileUtil.EXPORT_TO_SPREADSHEET_TITLE_DATE_FORMAT.format(finishDate), false);
-			activityDataRow[3] = new ExcelCell(getActivityDuration(learnerProgress, activity) / 1000,
-				false);
+			Long duration = getActivityDuration(learnerProgress, activity);
+			activityDataRow[3] = new ExcelCell(duration == null ? "" : duration / 1000, false);
 			activityDataRow[4] = new ExcelCell(activityArchive == null ? "" : activityArchive.getMark(),
 				false);