P: Message: "The catalog could not be opened due to an unexpected error."

Now, after a couple of days, I re-tried LrC 10.2 and (surprise!) it successfully opened my catalog. (21 March)

Strange.

I did not touch LrC, nor my files, folders or photos, in the intervening period.

This time, a "verifying integrity" message box popped up briefly before the catalog fully opened.

Understandably, I am quite "spooked" by this behavior. I will check periodically to see if this issue is really gone.

I am not a professional, and I (thankfully) don't use LrC for work. But I am photo enthusiast and I am naturally concerned about ~20 years of photos and edits.

@JPEG

Very same here 

Bummer. I re-tried opening my catalog about 7 hours after the "success" reported above and now it fails again.

I did not use LrC in the interim.

Summarizing, on macOS 10.15.7, I cannot open my catalog with LrC 10.2 -- even though it opened this morning. Weird.

I have been using Lightroom for at least 10 years, on both Mac and PC, and I have never seen anything like this.

Screenshot of error dialog below.

@Rikk Thanks. I followed these steps and they worked.

I also re-opened my new 10.2 catalog (using LrC 10.2) several additional times to be sure.

There must be something about the 5-minute wait time. During that wait time, the additional "*Sync" and "Mobile Downloads" files were magically created.

I will test daily for a few more days to be sure this fix has really taken hold.

Since the 10.2 update on Monday, this is the only report I can recall seeing. I would say this not a returned issue but likely a completely different issue. 

1. I would recommend opening your catalog in 10.1.1 and letting it sit idle for 5 minutes.
2. Close Lightroom 10.1.1
3. Make a copy of that catalog via the file system
4. Install 10.2.
5. Open the original catalog from step one
6. Screen shot the error. if it won't open and post it here.
7. If it fails, Zip the catalog from step 3 and I will send you instructions.

Commenting on my own post to add more info (sorry).

I rolled back to LrC 10.1.1 and my 10.1.1 catalog opens just fine. (I restored my 10.1.1 catalog via Time Machine.)

My 10.1.1 catalog did NOT open with 10.2. (Same "The catalog could not be opened due to an unexpected error." message)

I am on macOS Catalina 10.15.7

I have tried the double click and it fails. I have sent my lcat file to adobe and awaiitng a reply.  I have reverted to 10.1.1 and operational

Instead of starting Lightroom, go to the catalog and double click on it. That should automatically open Lightroom with that catalog.

If this does not work then try resetting your preferences file. There are are a multitude of examples on this forum as well as on the Lightroom Queen website.

Still not working, clear your previews. Hate to recommend that as it can take a long time to rebuild them.

Lastly there's the possibility that one of the Lightroom files is corrupt and that a reinstall is needed.

Hopefully someone else has a better idea.

Tip: hopefully you externalize all edits. If not, do that first. Then you can create a new catalog and import all your images without losing your edits. Edit history is lost but the final result is kept. Let's say that you moved the Contrast slider 3 times for a given image. History shows all  3 steps while only the net result is externalized. You will also lose your albums, create a keyword for each album and then you can easily recreate them through you will have lost your reordering.

I did not get a auto update msg. I just went into lrc help and did software update and was told there is a new version.

Where you updating from Lightroom Classic 10.1.1 version? Did Lightroom Classic prompted for an upgrade? I am sending an email off-list. We can investigate your catalog.

Thanks,
Sunil