When I try to back up Lightroom to my external hard drive, which I have been doing for the last 2 years, Lightroom won't backup the catalog & says "Lightroom was unable to back up the catalog named “Lightroom Catalog”. Please check your folder permissions, and make sure that you have available space on your backup drive and main catalog's drive." I have more than enough room on my hard drive. I am able to back up the catalog on my computer, but am now unable to work on more than one computer with Lightroom. Note: the current catalog size is 2.8mb & I have over 400mb available on my external hard drive. I have tried renaming the catalog, deleting the preview, deleting the lock file, restarting, & everything else I could think of. I have read/write permissions on the external hard drive. Thank you for your assistance!