Resource collection function

I am getting the following issue while running this service, 

var params = {
collectionName: "Mashups" /* STRING */,
principal: "CM_group" /* STRING */,
principalType: "Group" /* STRING */
};

// no return
Resources["CollectionFunctions"].AddCollectionVisibilityPermission(params);

Message :: Invalid Entity Type : Group/CM_group

while this is working good considering same principalType: "Group" 

var params = {
principal: "CM_group" /* STRING */,
allow: true /* BOOLEAN */,
resource: "*" /* STRING */,
type: "ServiceInvoke" /* STRING */,
principalType: "Group" /* STRING */,
collectionName: "Mashups" /* STRING */
};
// no return
Resources["CollectionFunctions"].AddCollectionRunTimePermission(params);