uninstalled program and reinstalled. This error appears when the program is started and won't allow me to go any further. I've been using LR5 for at least 6 months with no problem until today.
Using your system browser, go to the folder where your catalog is located and delete the folder with the extension .lrdata. Your preview folder has become damaged and needs to be replaced. In order to do that it is necessary for you to delete the old one. After you have done that, start Lightroom normally.