Hi Chris. Thanks for your reply. It is a relatively new ZODB from a fresh 2.8.0 installed a week or so ago. I went back over what I had been doing last evening with the site and it looks like something may have happened with a CMFBTree Folder instance - not sure exactly what at this point since there was no traceback. I am adding nested CMFBTreeFolders (3 levels) as part of a product using manage_addProduct a statements like the following. Is there anything wrong with this approach? btree_url0_folder_obj.manage_addProduct['BTreeFolder2'].manage_addConten t(type='CMF BTree Folder', id=btree_url1_folder_id) I removed the last instance I created last night and restarted and everything looks good again. Not sure it there is some sort of bug lurking but will be keep a close watch for any repeat of this in future. Thanks David