User profile is deleted each morning

I have a strange problem where a users profile is removed each morning.

I can set the profile up again on the local computer, copying the id file onto the computer and completing the setup. I can then start, stop and replicate the profile all day - it all works fine. The next morning, the user logs in and the profile is not working as the ID file has been removed. You have to copy another ID file into place and do the setup again.

This is also happening on a new and fresh computer.

Can anyone think of any reason why this might be happening ?