I've had LR 4 for more than 2 years. Worked just fine. Have not used for past year, as I have been traveling. Now, I cannot add new photos or video to my catalog. I have tried using my usual method of "Optimize Folder." Always freezes at 70%. Also tried via "Import into folder." Hit the same 70% wall. I sometimes get an "out of memory" error message, but not always.
Steps I've taken.
a. Reboot computer. (Obviously).
b. Ensure that LR is only program running.
c. Moved a ton of data from hard drive to an external hard drive (since error message did not specify what type of memory I was out of, I wanted to make sure I eliminated "not enough hard drive space" as an possible problem. I have more than 1 Terra-byte of available memory/space right now.
d. Uninstalled entire program, downloaded most recent version, and reinstalled it.