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

This thread is being merged into an existing authoritative thread for better tracking and response. Please review the official answer (if any) in the second post on the thread for more information. 

Unexpected error opening catalog. The catalog could not be opened due to an unexpected error.

How to fix this error?

Lr Classic 10.2 [202103041821-226a1211], MacOS 11.2.3 (20D91)

I sent @Rikk several corrupted catalogs. As a former software engineer you should be able to take that catalog and walk through the code to see where exactly it is breaking. There will only be certain conditions that trigger that error message. 

What was  interesting is that just prior to the corrupted catalog it reported a SQL error (the catalog is in a sql database)  therefore engineering should be able to find this problem

As I know with all bugs, unless you are a major customer seeing this, it goes to the back of the queue. Now if you are Peter Jackson trying to render a movie everyone is on it. Been involved in too many of those situations! 

I hope the Product Manager reads this and gives this bug some priority 

I tried it @Rikk when the problem reappeared and that didn't work either 

I am getting this error with increasing frequency. Rebooting my iMac seems to fix it an allow me to open the catalog, but that is a giant hassle and not always feasible. (April 24)

After almost two weeks for normal/correct behavior, my catalog once again failed to open today (April 23). (Same error message.)

@8510810, the first thing I tried was just rebooting my iMac. Then, after the reboot, the catalog opened just fine. (!!!)

So, due to this success, I was unable to execute the renaming test that you suggested.

I have not tried that

If you rename the offending catalog (and its associated Preview folders) does the problem disappear?

Same here, 10.2 can't open catalog, reverted to 10.1.1 and everything's back to normal.

The problem has returned for us again. We cannot open another catalog.

@Rikk you mentioned a thread in a previous post but I can't find it. Any update as we discussed this previously. Its clearly not a hardware issue with this many people experiencing a problem