I have had some permission issues when trying to chdir to a \\SERVERNAME\SHARENAME before. Keep in mind the cmd.exe does NOT support UNC paths so you can try and map a network drive.

I.e. net use \\servername\sharename /user:DOMAIN\username password

Something else to keep in mind is that in your script you may need to escape the \'s i.e. \\\\servername\\sharename, or alternately use /'s i.e. //servername/sharename

You did however mention Samba, so I asume that you are trying to access files, FROM a Win32 system, ON a Linux/Unix system. Could you not FTP the files you need to your Win32 system.