Starting LT presents this error message: you can click OK and get into LT but find thatProperties and other features do not function. The cause is usually after the use of a Windows Registry Cleaner that many websites tout as necessary.
In most circumstances, using that Registry Cleaner's Undo or Restore feature fixes the problem, most quality products also include an exclusion option where you can add AutoCAD/LT to the list of programs not to touch.
If you use a freebie or a bargain cleaner, they don't restore or recover well. A repair reinstall of LT fixes the problem as noted HERE.
If not, you need to go a step further and completely uninstall all Autodesk products on your system as discussed HERE, then reinstalling them after a Windows restart.
Click on this for a GOOGLE search on the topic and other solutions posted.
Don't forget to backup all your LT customizations first, often, and regularly.