Thanks again for yor answer!
I have now tried all three options to reset my LCC preferences. But my problem remains.
I have also tried to use new folder for the backup file, without any good result.
I always get tte message "Failed to backup directory "Ligtroom...."". Check folder permissions and make sure you have enough space on the backup and main directory drive.
Frustrating 😞
This is the first time that you say that the backup itself fails! So far, you only mentioned getting that error message about the missing location. If the backup itself fails, then the problem is corruption in your catalog. The backup frequency and backup location are stored in the catalog settings, so this is probably one and the same problem. I have seen this a few times in this forum, and here's how you can normally fix this:
1: Create a brand new catalog.
2: Verify that you can backup this new catalog.
3: Choose 'File - Import from Another Catalog' and select your old catalog.
4: In the dialog that follows, select to import all new photos but do not move them.
5: This will create a copy of your old catalog. Check that you can still make a backup.
If all is well, then this will be your new catalog from now on. If you synced your old catalog, you will have to sync this one. If you used publishing services, you will have to recreate these because those are the only things that won't import.