A customer called with a  laptop that would not connect to any mapped drives.   Investigating found that attempting to map via name would not work but mapping via IP did work.  DNS was working properly and the file server would ping by name or IP.  Logged in with an administrator account and all mapped drives came up properly.   Finally discovered that this machine had not been on the domain for some months and there were old cached credentials for the file server in stored credentials.  These are stored by path so it was using those credentials by default when attempting to map by name but not when mapping by IP.  Removal of these stored credentials allowed the mapping to complete properly.