In connection with moving to a new macbookpro, I have copied my images, catalog and settings to the new computer from an external drive connected to my old computer. Double clicking on the lrcat file on the new computer, it reports 'cannot connect...' as expected. When "choose a different catalog' and browsing to the root folder on the new computer, the choose button is grayed out, as it also is for all the sub-folders. There is no error message. There is a note that warns against network volumes and read-only folders. The data are not on a network volume, and the permissions grant me (administrator) read/write access.
I have performed the first-aid function in Disk Utilities.