Lightroom Classic Keywording error 1555

I’m writing this post in case readers of these articles come across a similar issue and so can see the steps I have taken to try to resolve it. So far unsuccessfully, I’m afraid. If you have any suggestions, please let me (and other people with this issue) know in the comments.

I’ve been running Lightroom Classic for many years on Windows 10 and now 11 and the app is up to date. I have increasingly been seeing an error code 1555 which refers to a “UNIQUE constraint failed” when synchronizing keywords and other metadata between images in the catalog. Screenshot of the error message (which is always the same) is here.

This started around the beginning of 2025 and does not occur each time I sync metadata. I would estimate that I can sync information between 5 and 10 times before the error occurs.

Update 1: A comment below reminded me that I used to have a relatively similar issue throughout 2024. I would be sync’ing metadata between images and it would all work with no issues and then suddenly it would stop working. No errors or any other indication of a problem – the metadata would not be copied. The only solution was to restart Lightroom. That all makes me think that there is an ongoing bug in LR that has been there for some time and all that happened earlier in the year was that an error message has been added when it occurs. The error message is quite generic – normally a complete error message would have the values that it was trying to write in the message itself I think. Maybe this means that Adobe are working on it and want to see when it occurs – or is that wishful thinking!

But back to the current issue with the error message. I then have to close LR to get it to work again. I have started testing the integrity of the catalog when restarting LR, which you can do by holding down the Alt key as you click on the LR icon. This lets you choose which catalog to open and also gives the option to check and repair the database. Most times it shows a corrupt catalog and starts a repair process for the catalog, which is successful, and I can start work again.

In the past 24 hours, it has failed four times to this error (and so I have 4 corrupt catalogs on my hard drive).

During earlier support calls, we have created a new catalog from scratch and imported all information for my 140,000 images into it. This took many hours, and for a time, I thought the problem had been resolved, but it came back after a few days. I am currently working with that rebuilt catalog.

I also logged out of and back into the Creative Cloud App and confirmed there were no updates pending. I have uninstalled LR Classic and all preferences, restarted my PC and then installed the App again. Once again, the metadata sync has failed, and the catalog was found to be corrupt again.

I also downloaded my entire keyword list from LR and went through it looking for anything strange. I have 23,000 keywords! You can export this as a CSV and import into Excel and there is a formula I found to identify non-alphanumeric characters in an Excel cell. There were a few unusual characters in there that got in either by copying something from the web, or mistyping. Things like jæren and kÄ«lauea. I have deleted those from LR and any images that used them. I thought that might help – but no.

I also tried the File:Optimize Catalog command. After using that, the error appeared on the second use of Sync Metadata.

Building on my relatively vague understanding of SQL databases, I think that rather than storing all the keywords themselves in a table associated with a specific image, there is one master list of keywords and a unique index against each one. The index is then stored with each image. For that to work, this table of keywords must be unique – ie no keyword should appear more than once in the table. It sounds as though something is causing a second copy of the same keyword into that table breaking the Unique constraint. Any other ideas gratefully received.

One more update – I did a lot of sync’ing of metadata this afternoon but I only selected the Title and Caption to copy to the new images. Everything worked without any issues but of course it meant that I had to copy and then paste the keywords separately. That worked OK – it is not as smooth as sync’ing all metadata, but it at least didn’t mean I had to stop to close and reload Lightroom!

I’ll probably try with Adobe support agents again later this week, but it takes quite a lot of time getting the new agent up to speed, even though there is a case number.