Index: lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/web/controller/LearningController.java
===================================================================
diff -u -rbdd3abc4e8371ce227cb000d5aac58fdb45077a5 -r7eab6b4371036949ed61a387bc7706473895f567
--- lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/web/controller/LearningController.java	(.../LearningController.java)	(revision bdd3abc4e8371ce227cb000d5aac58fdb45077a5)
+++ lams_tool_assessment/src/java/org/lamsfoundation/lams/tool/assessment/web/controller/LearningController.java	(.../LearningController.java)	(revision 7eab6b4371036949ed61a387bc7706473895f567)
@@ -1152,8 +1152,18 @@
 	// Criterion gets automatically created and there must be only one.
 	List<RatingCriteria> criteria = ratingService.getCriteriasByToolContentId(assessment.getContentId());
 	if (criteria.size() >= 2) {
-	    throw new IllegalArgumentException("There can be only one criterion for an Assessment activity. "
-		    + "If other criteria are introduced, the criterion for rating other groups' answers needs to become uniquely identifiable.");
+	    try {
+		for (int criterionIndex = 1; criterionIndex < criteria.size(); criterionIndex++) {
+		    RatingCriteria criterion = criteria.get(criterionIndex);
+		    Long criterionId = criterion.getRatingCriteriaId();
+		    userManagementService.delete(criterion);
+		    log.warn("Removed a duplicate criterion ID " + criterionId + " for Assessment tool content ID "
+			    + assessment.getContentId());
+		}
+	    } catch (Exception e) {
+		log.warn("Ignoring error while deleting a duplicate criterion for Assessment tool content ID "
+			+ assessment.getContentId() + ": " + e.getMessage());
+	    }
 	}
 	ToolActivityRatingCriteria criterion = null;
 	if (criteria.isEmpty()) {
Index: lams_tool_doku/src/java/org/lamsfoundation/lams/tool/dokumaran/service/DokumaranService.java
===================================================================
diff -u -r0b845931db55d90f0dcabc0b33cce5c7df688153 -r7eab6b4371036949ed61a387bc7706473895f567
--- lams_tool_doku/src/java/org/lamsfoundation/lams/tool/dokumaran/service/DokumaranService.java	(.../DokumaranService.java)	(revision 0b845931db55d90f0dcabc0b33cce5c7df688153)
+++ lams_tool_doku/src/java/org/lamsfoundation/lams/tool/dokumaran/service/DokumaranService.java	(.../DokumaranService.java)	(revision 7eab6b4371036949ed61a387bc7706473895f567)
@@ -420,9 +420,14 @@
 	Map<Long, ItemRatingDTO> itemRatingDtoMap = null;
 	if (dokumaran.isGalleryWalkStarted()) {
 	    if (!dokumaran.isGalleryWalkReadOnly()) {
-		// it should have been creating on lesson create,
+		// it should have been created on lesson create,
 		// but in case Live Edit added Gallery Walk, we need to add it now, but just once
-		createGalleryWalkRatingCriterion(dokumaran.getContentId());
+		try {
+		    createGalleryWalkRatingCriterion(dokumaran.getContentId());
+		} catch (Exception e) {
+		    log.warn("Ignoring error while processing Dokumaran Gallery Walk criteria for tool content ID "
+			    + dokumaran.getContentId());
+		}
 	    }
 
 	    // Item IDs are DokumaranSession session IDs, i.e. a single Etherpad
@@ -519,13 +524,27 @@
 
     private List<RatingCriteria> createGalleryWalkRatingCriterion(long toolContentId) {
 	List<RatingCriteria> criteria = ratingService.getCriteriasByToolContentId(toolContentId);
+
 	if (criteria.size() >= 2) {
+	    criteria = ratingService.getCriteriasByToolContentId(toolContentId);
 	    // Dokumaran currently supports only one place for ratings.
 	    // It is rating other groups' pads on results page.
 	    // Criterion gets automatically created and there must be only one.
-	    throw new IllegalArgumentException("There can be only one criterion for a Dokumaran activity. "
-		    + "If other criteria are introduced, the criterion for rating other groups' answers needs to become uniquely identifiable.");
+	    try {
+		for (int criterionIndex = 1; criterionIndex < criteria.size(); criterionIndex++) {
+		    RatingCriteria criterion = criteria.get(criterionIndex);
+		    Long criterionId = criterion.getRatingCriteriaId();
+		    dokumaranDao.delete(criterion);
+		    log.warn("Removed a duplicate criterion ID " + criterionId + " for Dokumaran tool content ID "
+			    + toolContentId);
+		}
+	    } catch (Exception e) {
+		log.warn("Ignoring error while deleting a duplicate criterion for Dokumaran tool content ID "
+			+ toolContentId + ": " + e.getMessage());
+	    }
+	    return criteria;
 	}
+
 	if (criteria.isEmpty()) {
 	    ToolActivityRatingCriteria criterion = (ToolActivityRatingCriteria) RatingCriteria
 		    .getRatingCriteriaInstance(RatingCriteria.TOOL_ACTIVITY_CRITERIA_TYPE);
Index: lams_tool_doku/src/java/org/lamsfoundation/lams/tool/dokumaran/web/controller/LearningController.java
===================================================================
diff -u -r53041ab71ac581668c14bdf40f65be5ea5f26961 -r7eab6b4371036949ed61a387bc7706473895f567
--- lams_tool_doku/src/java/org/lamsfoundation/lams/tool/dokumaran/web/controller/LearningController.java	(.../LearningController.java)	(revision 53041ab71ac581668c14bdf40f65be5ea5f26961)
+++ lams_tool_doku/src/java/org/lamsfoundation/lams/tool/dokumaran/web/controller/LearningController.java	(.../LearningController.java)	(revision 7eab6b4371036949ed61a387bc7706473895f567)
@@ -59,6 +59,7 @@
 import org.lamsfoundation.lams.web.util.AttributeNames;
 import org.lamsfoundation.lams.web.util.SessionMap;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.orm.hibernate5.HibernateOptimisticLockingFailureException;
 import org.springframework.stereotype.Controller;
 import org.springframework.web.bind.annotation.ModelAttribute;
 import org.springframework.web.bind.annotation.RequestMapping;
@@ -203,7 +204,14 @@
 	}
 
 	if (dokumaran.isGalleryWalkStarted()) {
-	    List<SessionDTO> groupList = dokumaranService.getSummary(dokumaran.getContentId(), user.getUserId());
+	    List<SessionDTO> groupList = null;
+	    try {
+		groupList = dokumaranService.getSummary(dokumaran.getContentId(), user.getUserId());
+	    } catch (HibernateOptimisticLockingFailureException e) {
+		log.warn("Ignoring error caused probably by creating Gallery Walk criteria", e);
+		// simply run the transaction again
+		groupList = dokumaranService.getSummary(dokumaran.getContentId(), user.getUserId());
+	    }
 	    request.setAttribute(DokumaranConstants.ATTR_SUMMARY_LIST, groupList);
 
 	    if (currentUserDto == null) {