Mapped Network Shares Disappear

We have 3 Vista machines running in our office. A login script takes care of
our mapped drives, etc. This user logs in fine with connection to all
network drives. However, after some time her mapped drives disappear. I
don't mean disconnected either - they just don't show up anymore. Running
the login script sometimes works but the drives sometimes don't appear until
anywhere from 5 minutes to 5.5 hours later. Please help. If this is some type
of "functionality" I'd love to turn it off or change it.

Thank you.