Lightroom is not able to read the preview cache files causing this error.
Please follow the below steps.
> Quit Lightroom
> Navigate to the catalog location. (By default, Pictures folder is the location of the catalog)
> Rename the folders containing Previews.lrdata
> Click on the .LRCAT file to launch Lightroom
Let me know if this helps.
Worked for about 1/2 an hour or so. then back to the same error
Please follow the steps provided above.
Also, please tell me where exactly you have stored your Lightroom catalog and the images.
Not nearly as well organized as I'd like. When I deleted the extra catalogs and preview files it was a bit over 6 gig