diff --git a/src/main/java/org/olat/core/commons/services/mark/impl/ui/MarkController.java b/src/main/java/org/olat/core/commons/services/mark/impl/ui/MarkController.java
index 5f5f1c7c879c38801ab36b69ca8e5091188a26c3..ff41acd5003162d77ae7b898c4e215dd5ef5d3fd 100644
--- a/src/main/java/org/olat/core/commons/services/mark/impl/ui/MarkController.java
+++ b/src/main/java/org/olat/core/commons/services/mark/impl/ui/MarkController.java
@@ -103,6 +103,7 @@ public class MarkController extends FormBasicController {
 	protected void initForm(FormItemContainer formLayout, Controller listener, UserRequest ureq) {
 		markLink = uifactory.addFormLink("mark", " ", " ", formLayout, Link.NONTRANSLATED + Link.LINK_CUSTOM_CSS);
 		markLink.setCustomEnabledLinkCSS(marked ? "b_mark_set" : "b_mark_not_set");
+		markLink.setEnabled(!ureq.getUserSession().getRoles().isGuestOnly());
 
 		String tooltip;
 		if(stat == null) {
diff --git a/src/main/java/org/olat/modules/fo/FilterForUserController.java b/src/main/java/org/olat/modules/fo/FilterForUserController.java
index ec765ee7e229b198363e3bffa3bf306216e15d1f..597ca831485a8fcc18bedffa7dc712e61372ae01 100644
--- a/src/main/java/org/olat/modules/fo/FilterForUserController.java
+++ b/src/main/java/org/olat/modules/fo/FilterForUserController.java
@@ -406,11 +406,13 @@ public class FilterForUserController extends BasicController {
 		MarkResourceStat stat = stats.get(subPath);
 		MarkingService markingService = (MarkingService)CoreSpringFactory.getBean(MarkingService.class);
 		
-		String businessPath = currentMark == null ?
-				getWindowControl().getBusinessControl().getAsString() + "[Message:" + m.getKey() + "]"
-				: currentMark.getBusinessPath();
-		Controller markCtrl = markingService.getMarkController(ureq, getWindowControl(), currentMark, stat, forumOres, subPath, businessPath);
-		vcThreadView.put("mark_"+msgCount, markCtrl.getInitialComponent());
+		if(!ureq.getUserSession().getRoles().isGuestOnly()) {
+			String businessPath = currentMark == null ?
+					getWindowControl().getBusinessControl().getAsString() + "[Message:" + m.getKey() + "]"
+					: currentMark.getBusinessPath();
+			Controller markCtrl = markingService.getMarkController(ureq, getWindowControl(), currentMark, stat, forumOres, subPath, businessPath);
+			vcThreadView.put("mark_"+msgCount, markCtrl.getInitialComponent());
+		}
 		
 		map.put("modified", dateFormat.format(m.getLastModified()));
 		// message attachments
diff --git a/src/main/java/org/olat/modules/fo/ForumController.java b/src/main/java/org/olat/modules/fo/ForumController.java
index d81cb747e7632353cd956c8234ae9a3ca2bdd25c..83eb9a660220fd786e1ed12cc83b59341811a8c0 100644
--- a/src/main/java/org/olat/modules/fo/ForumController.java
+++ b/src/main/java/org/olat/modules/fo/ForumController.java
@@ -1181,15 +1181,17 @@ public class ForumController extends BasicController implements GenericEventList
 		MarkResourceStat stat = stats.get(subPath);
 		MarkingService markingService = (MarkingService)CoreSpringFactory.getBean(MarkingService.class);
 		
-		String businessPath = currentMark == null ?
-				getWindowControl().getBusinessControl().getAsString() + "[Message:" + m.getKey() + "]"
-				: currentMark.getBusinessPath();
-		Controller markCtrl = markingService.getMarkController(ureq, getWindowControl(), currentMark, stat, forumOres, subPath, businessPath);
-		vcThreadView.put("mark_"+msgCount, markCtrl.getInitialComponent());
+		if(!ureq.getUserSession().getRoles().isGuestOnly()) {
+			String businessPath = currentMark == null ?
+					getWindowControl().getBusinessControl().getAsString() + "[Message:" + m.getKey() + "]"
+					: currentMark.getBusinessPath();
+			Controller markCtrl = markingService.getMarkController(ureq, getWindowControl(), currentMark, stat, forumOres, subPath, businessPath);
+			vcThreadView.put("mark_"+msgCount, markCtrl.getInitialComponent());
+		}
 		
-		businessPath = BusinessControlFactory.getInstance().getAsString(getWindowControl().getBusinessControl()) + "[Message:" + m.getKey() + "]";
 		if (uIsMsgC) {
 			OLATResourceable messageOres = OresHelper.createOLATResourceableInstance("Forum", m.getKey());
+			String businessPath = BusinessControlFactory.getInstance().getAsString(getWindowControl().getBusinessControl()) + "[Message:" + m.getKey() + "]";
 			Controller ePFCollCtrl = EPUIFactory.createArtefactCollectWizzardController(ureq, getWindowControl(), messageOres,
 					businessPath);
 			if (ePFCollCtrl != null) {