• If Lumion fails to load or displays an error while loading an .LS Project file it usually means that there has been a problem due to a save error. 
• If Lumion displays an error while saving or overwriting a Project file, it usually means that something on the PC is preventing the save/overwrite operation. 

Please see this article for suggestions to help with saving and loading Projects:

• Knowledge Base: Why might Lumion not open or display an error when you load, save or overwrite a Project file?