Today’s Question: I am encountering this error message when exporting a catalogue: “Lightroom encountered an error when reading from its preview cache and needs to quit.” Any advice as to why and what the remedy is.
Tim’s Quick Answer: This error message indicates that the previews file has become corrupted. You will need to delete the previews and have Lightroom rebuild them.
More Detail: In the folder where your Lightroom catalog is stored, there is also a “Previews” file. Only the Previews file should be deleted, leaving all other files where they are. In particular, you need to be careful not to delete the “lrcat” file, which is your actual Lightroom catalog.
To locate the folder containing your catalog, you can choose Catalog Settings from the menu. This is found on the Edit menu on Windows and on the Lightroom menu on Macintosh. On the General tab in the Catalog Settings dialog you can click the Show button to open a window in your operating system showing you the folder that contains your catalog. Close Lightroom before deleting the Previews file.
Then open the folder that contains the Lightroom catalog. You will see a file that has the same base filename as your catalog, followed by “Previews.lrdata”. That file with the “Previews.lrdata” ending is the only file you need to delete. You can also move it to a different location if you want to be extra cautious.
After deleting (or moving) the Previews file, re-launch Lightroom. Initially there won’t be previews for any of your images, but Lightroom will generate them again as you browse the photos. You can also generate them all in one process, though it will require considerable time depending on how many images are in your catalog.
To build previews for all photos in your catalog, first make sure all hard drives used to store photos for your Lightroom catalog are connected. Then select the All Photographs collection in the Catalog section of the left panel in the Library module, and make sure there aren’t any filters applied that would cause you to only see a portion of your photos. Then choose Edit > Select All from the menu to select all photos. Finally, choose Library > Previews > Build Standard-Sized Previews from the menu. Lightroom will then generate previews for all photos, with the progress shown on the identity plate at the far left side of the top panel.