The credentials file should be in the form
In the man page(http://www.samba.org/samba/docs/man/manpages-3/smbclient.1.html) is says "username", not "user"
Also, it should be mentioned that the password cannot be followed by a newline, and it must be the last thing in the file(in the example in the manual, it has a newline after it, to add the domain)
In current Samba the parsing matches the documentation of
username = value
password = value
domain = value
The parsing is in cli_credentials_parse_file() and this is the new common routine.