Just bought LR6 to run on new iMac desktop - it is not recognizing my old catalogs and/or showing only a few images - the placeholders are there, the image counter is there but there is no image and it will not open. I don't want to have to go back and redo everything. Has anyone else encountered this problem?
Not sure what you mean by "not recognizing my old catalogs". When you use LR6 to open catalogs created by earlier versions, you will be prompted to migrate the old catalog to a new LR6-format catalog, which will be given a new name.
Because this is a new catalog, all new previews and thumbnails will be created; thus you will need access to the original files (need to plug-in your external hard drives, etc).