Could you please let me know the version of Lightroom installed on your computer ?
Also please let me know the workflow that you follow ?
You don't need to back up the previews, Lightroom can recreate them anytime, and will also create previews for new files as needed.
The previews folder can also be many gigabytes, depending on how many images are in the catalog, and how large they are.
(I have 17,000 images, and the previews folder is 5.4 gb)
So I would set the backup software to exclude the previews folder.
I'm using Lightroom CC 2015.3
My workflow: For each shooting I generate a new catalog, importing the RAW, do all the work necessary (incl.Photoshop) and finally export the stuff. The material is synchronized from my Lenovo T550 on to the server and from there to my Desktop-Computer. There I'll continue to work with the material. So I have three versions of the material Laptop, Server and Desktop to be on the save side. The software for the synchronization is BestSync 2015.
What is so weird is, that only the *.lrprev files are making trouble. Everthing else works fine.
It is not recommended to store the Catalog on Server.
Also you may rename the Previews.lrdata and then Lightroom will recreate the previews file.
Sorry misunderstanding: I'm not working with the catalog from the server. Wether on Laptop or Desktop, there is always everything local. The server is just the medium were both exchanged the data and by that I have automatically a backup.
I also checked, that preview files from an older LR-version are synced without any problem.
Thanks Tanuj for spending your time on this weird issue......
LR doesn't control what you backup or where you back it up to. So look at the software you are using to do the backups and the PATH it is look for the Previews folder. Also check the previews folder for Read and Write permissions