[Samba] valid users and lost password on windows xp

[Luca Ferrari]

Hi all,
in my network we're using samba as a disk share for users. Each user can 
access users thru his unix login name and password, but sometimes I 
experience that Windows xp (prof.) loses the password, so it prompts the user 
again for the it. In particular, after a smbpasswd password change, I have 
one machine that, even if mounting the share as a network disk (with username 
and password specified and the checkbox to store at reboot is checked) each 
day requires the user to insert the password. In particular the computer 
always proposes a default username composed by 
\\computer_name\windows_username.
Is there any way to fix this problem? Anyone knows where and how to interact 
with the stored network-password in a windows system?

Thanks,
Luca