Do you have 2 versions of Lightroom on your computer? This message appears when you use an older version of LR (LR 5) to open a catalog created by a newer version (LR 6). Lightroom catalogs are not backwards compatible.
Thanks. I did not realize before I have two versions. I only installed once. I will remove the old version. Thanks again.
Fortunately, there is a quick and easy solution to this problem. If you encounter this error message on startup then all that you need to do is to tell your computer to open this Lightroom Catalog (your .lrcat file) using the most recently installed version of the Lightroom Application.
In the Mac world, this is best done by right-clicking on your .lrcat file and using the <em>Open With</em> command. Windows users will find the same command with a right-click although so far I have mostly seen this error on computer's running the Mac operating system. See the video tutorial below for more assistance resolving this issue.