How do you connect / attempt to connect ?
I normally use "Connect to Server" in the "Go" menu in the Finder. Then specify the Windows server by IP in the box, ie.
ftp://10.0.0.28/ . This should be enough.
If you're specifying a name, rather than IP, it may be incorrectly spelt or punctuated.
The Windows Server may also require an unconventional port be used for FTP access.
Or, it may require secure FTP be used, use s
ftp://10.0.0.28/.