diff --git a/src/main/java/org/gcube/data/access/storagehub/services/GroupManager.java b/src/main/java/org/gcube/data/access/storagehub/services/GroupManager.java
index 04aaee4..037e2cf 100644
--- a/src/main/java/org/gcube/data/access/storagehub/services/GroupManager.java
+++ b/src/main/java/org/gcube/data/access/storagehub/services/GroupManager.java
@@ -37,6 +37,7 @@ import org.gcube.common.gxrest.response.outbound.GXOutboundErrorResponse;
 import org.gcube.common.scope.api.ScopeProvider;
 import org.gcube.common.storagehub.model.acls.AccessType;
 import org.gcube.common.storagehub.model.exceptions.BackendGenericError;
+import org.gcube.common.storagehub.model.exceptions.InvalidCallParameters;
 import org.gcube.common.storagehub.model.exceptions.InvalidItemException;
 import org.gcube.common.storagehub.model.exceptions.UserNotAuthorizedException;
 import org.gcube.common.storagehub.model.types.NodeProperty;
@@ -45,6 +46,7 @@ import org.gcube.data.access.storagehub.Constants;
 import org.gcube.data.access.storagehub.Utils;
 import org.gcube.data.access.storagehub.exception.MyAuthException;
 import org.gcube.data.access.storagehub.handlers.CredentialHandler;
+import org.gcube.smartgears.utils.InnerMethodName;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -64,7 +66,9 @@ public class GroupManager {
 	@Path("")
 	@Produces(MediaType.APPLICATION_JSON)
 	public List<String> getGroups(){
-
+		
+		InnerMethodName.instance.set("getGroups");
+		
 		JackrabbitSession session = null;
 		List<String> groups= new ArrayList<>();
 		try {
@@ -98,7 +102,8 @@ public class GroupManager {
 	@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
 	@AuthorizationControl(allowedRoles={VREMANAGER_ROLE}, exception=MyAuthException.class)
 	public String createGroup(@FormParam("group") String group, @FormParam("accessType") AccessType accessType){
-
+		
+		InnerMethodName.instance.set("createGroup");
 				
 		JackrabbitSession session = null;
 		String groupId = null;
@@ -131,7 +136,9 @@ public class GroupManager {
 	@Path("{group}")
 	@AuthorizationControl(allowedRoles={VREMANAGER_ROLE}, exception=MyAuthException.class)
 	public String deleteGroup(@PathParam("group") String group){
-
+		
+		InnerMethodName.instance.set("deleteGroup");
+		
 		JackrabbitSession session = null;
 		try {
 			
@@ -165,7 +172,9 @@ public class GroupManager {
 	@Consumes(MediaType.APPLICATION_FORM_URLENCODED)
 	@AuthorizationControl(allowedRoles={VREMANAGER_ROLE}, exception=MyAuthException.class)
 	public boolean addUserToGroup(@PathParam("id") String groupId, @FormParam("userId") String userId){
-
+		
+		InnerMethodName.instance.set("addUserToGroup");
+				
 		JackrabbitSession session = null;
 		boolean success = false;
 		try {
@@ -178,7 +187,10 @@ public class GroupManager {
 
 			Group group = (Group)usrManager.getAuthorizable(groupId);
 			User user = (User)usrManager.getAuthorizable(userId);
-
+			
+			if (group.isMember(user))
+				throw new InvalidCallParameters("user "+userId+" is already member of group "+groupId);
+			
 			success = group.addMember(user);
 
 			String folderName =  group.getPrincipal().getName();
@@ -204,7 +216,9 @@ public class GroupManager {
 	@Path("{groupId}/users/{userId}")
 	@AuthorizationControl(allowedRoles={VREMANAGER_ROLE}, exception=MyAuthException.class)
 	public boolean removeUserFromGroup(@PathParam("groupId") String groupId, @PathParam("userId") String userId){
-
+		
+		InnerMethodName.instance.set("removeUserFromGroup");
+		
 		JackrabbitSession session = null;
 		boolean success = false;
 		try {
@@ -217,7 +231,10 @@ public class GroupManager {
 
 			Group group = (Group)usrManager.getAuthorizable(groupId);
 			User user = (User)usrManager.getAuthorizable(userId);
-
+			
+			if (!group.isMember(user))
+				throw new InvalidCallParameters("user "+userId+" is not member of group "+groupId);
+			
 			//delete folder on user
 			String folderName =  group.getPrincipal().getName();
 			Node folder = getVreFolderNode(session, folderName);
@@ -250,7 +267,9 @@ public class GroupManager {
 	@Produces(MediaType.APPLICATION_JSON)
 	@AuthorizationControl(allowedRoles={VREMANAGER_ROLE}, exception=MyAuthException.class)
 	public List<String> getUsersOfGroup(@PathParam("groupId") String groupId){
-
+		
+		InnerMethodName.instance.set("getUsersOfGroup");
+		
 		JackrabbitSession session = null;
 		List<String> users = new ArrayList<>();
 		try {