Go to the location where your Lightroom catalog is stored and get rid of the previews file with the name Previews.lrdata (not the .lrcat file )
By default, it is stored under Pictures\Lightroom
Let us know if that helps.
Thanks for the suggestion but I don't want to delete the previews file. I accidentally found a solution that seems to work. By opening LR from the Pictures folder on my PC I haven't had the problem.
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You should delete that previews.lrdata file. It won't do any harm and it will solve the problem.