When you change password on LPAR and then you notice problem when you try to connect to IFS from Windows computer. There is probably problem with old credentials stored on Windows system.
You can show actual credential on Windows and you will get something like this
C:\Users\myusername>net use
New connections will be remembered.
Status Local Remote Network
-------------------------------------------------------------------------------
OK Y: \\pgfil01\Departments Microsoft Windows Network
OK Z: \\projects\public Microsoft Windows Network
OK \\ibm1\IPC$ Microsoft Windows Network
you can delete stored credential using this command
net use \\ibms1\IPC$ /delete
don't forget check if user profile isn't blocked on your LPAR (you can use Navigator)