Repeated prompt for password

I have a XP ftp server running ServU ftp server version 6.

All clients connect to it via the lan: ftp://server or internet
ftp://outsidetoserver.


Users can browse the folders set up in ServU, and XP users even with
IE7 can open a word document for example.


However Vista users cannot. They get as far as seeing the word
document then when they double-click to open it repeatedly asks for
username and password. Even if I type the ServU administrator or the
administrator of the box username and password it just does the same.


I have tried lowering the security settings of IE7, upgrading ServU
to
version 7 and nothing seems to work. There's nothing in event logs
either.

Thanks!