Mapped drive disappears won't stay mapped persistently

We use network drives sometimes they will not stay after a reboot. I had this problem and could not work out the problem. There was a faulty login script under the users profile in the Active Directory. It's a good place to check. We had moved domains a while back and some users have the old path, meaning the login script was removing the good working path and then failing to connect to it's incorrect one leaving nothing mapped.