You need to delete the Preview Cache for your Lightroom catalog.
It is located in the same folder as the Lightroom Catalog. The preview cache name ends with Previews.LRDATA and should be deleted. Do not confuse this with *.LRCAT, which should not be deleted.Below is the image of what it is named as Default LightroomcatalogPreviews.Lrdata.
Location /Pictures/Lightroom on Mac and My Pictures\Lightroom on Windows Pictures/Lightroom on MAC
Delete this Folder and restart Lightroom
Let us know if that helps
i delteted this folder and it still didnt work
Then you didn't delete the right folder.
It's possible to have more than one catalogue. So look for other catalogues (*.lrcat files) and their previews folders. Delete those. It doesn't do any harm because Lr will rebuild previews as needed.
It work!!! thanks