Change password at startup

I have a small business network which is on a workgroup
with several XP Pro machines. All the machines work great
except for one. One machine asks for the network password
to be changed every 7 days or so. None of the machines
have network passwords and should just go directly into
windows. This one does go directly into windows with the
exception of the requested password change now and again.
Any ideas?

Thanks,

Justin