Have you ever done ScanDisk since that error appeared... just as a sugestion...

Are you using Norton Antivirus ???
Have you got any messages of infected files? (if yes than Norton Antivirus is not letting LW to acces that files anymore... and there is the reason for the error)

(Only after scaning your files with an antivirus) go to Library->Incomplete Files and try to Launch your files and see in what condition they are... (I think that they are 100% on your hard disk)