When you usually get this error message you have a User ID that is mapped to a security ID (SID) no longer exists on your computer and is reporting the error.
Each user, group or object has a Security Id or identifier. Example: You may have a user name that was in a application and that user name is no longer valid or has been
renamed but the application is still referencing that name. So it reports an error. You may have to go back and change back to the original name or remove the name from
the problem application.
here for an article that explains it a little better.