After upgrading from 4.4 to 5.5 i get a message 'lightroom has encountered an error when reading from its preview cache and needs to quit, any ideas please, thanks.
Using your operating system, find the cache, it is a Folder whose name ends with Previews.LRDATA and delete it. (do not delete the .LRCAT file)
Then open Lightroom.
ill give it a whirl thanks