Is someone else accessing the file? Did a recent MicroStation session terminate abnormally?
Each time a drawing is opened, MicroStation creates a text file in the project directory containing the user’s name and time the file was opened. The file will have the same name as the DGN in question with a .LOK file extension. These files are deleted at the end of the MicroStation session. If a MicroStation session is aborted abnormally the files will be left behind.