Do you know if he is using the same version of Access as everyone else?
Also, you say you split the database - so that means you have a linked Front and Back, correct? Make sure the user has the same path and has permission to open the file in the folder they save it to.

One more thing - it sounds like the users are using Runtime which is why the application shuts down. If you add error traps to all your code then the error would be a bit more helpful.