I have lightroom 4.4 and when it launches I get the error message "lightroom encountered an error when reading from it's preview cache and needs to quit. It will fix this problem next time it launches. Then it closes the program. I have deleted the program and reinstalled it, nothing happens. Tried resetting my computer to an earlier point before it updated and nothing happened. Can anyone help?
In the folder containing your LR catalog there is also a folder called Previews.lrdata (with the catalog name in front of Previews).
Delete this folder - don't delete anything else. (the .lrcat file is your catalog, don't delete that!)
Lightroom should now work, and will rebuild all the previews.