If you create a collection with no search criteria - (Go to Search menu>New collection>name it) you can't edit the criteria of that collection later as somewhat indicated in the Meridian Users Guide on page 94 under the heading "To edit the criteria of an existing collection". You can add files to it by finding them first, selecting them and adding them though. I suggest updating the users guide to make that more clear. ​​​Maybe even hide the edit button, since there is nothing you can do with it anyway.