I am in my main catalog, not a backup.
How do you know this? If you go to Catalog Settings and examine the exact name and folder location of the catalog in use, is that the location and name of your main catalog or a backup?
You have to open the same catalog (original) which is syncing with the mobile application to get rid of that message.
If you were recently working on the main catalog and switched to your backup catalog by mistake.
Please go to File> Open recent and launch your main catalog.
Thanks for your replies. It looks like I've sorted it out now.
I was in the main catalog, not a back up.
The issue appeared to be with 1 particular collection. By un-syncing that collection, Lightroom connected to Lightroom Mobile. I allowed it to remove the files from the cloud then re-synced the collection. It appears to be functioning correctly now.
I realize that this thread is over a year old, but I just started Lightroom CC and am encountering the same ("appears to be a backup catalog) error. I have tried deleting all I am hoping that you might still respond.
I suspect part of my problem might be that I created my primary catalog in Lightroom 4, before upgrading to Lightroom 5 with my CC membership (yestereday). For reasons I don't recall, I also have a Lightroom 5 catalog, but it contains only a handful of images. In other words, I have been using the Lightroom 4 catalog as my "primary" catalog, but a 5 catalog exists.
Can you help me to sort this out?