The issue may not be related to the number of records or how they were copied into the “groups” (which I think you’re referring to as “folders” and “subfolders”) - but rather how you created the groups (folders/subfolders). If you used “group sets” that may be the problem why you cannot create a combination group. Only custom groups and smart groups, not group sets, can be used to create combination groups. For further information go to the Endnote toolbar, click Help and look up “Combination groups” and “Groups”.