Information can be found here on how to fix it:
http://wiki.samba.org/index.php/Windows7Additionally if the version of Samba is old enough, you need to disable requiring 128 bit encryption.
To do that:
Control Panel - Administrative Tools - Local Security Policy
Local Policies - Security Options
Network security: LAN Manager authentication level
Send LM & NTLM responses
Minimum session security for NTLM SSP
Disable Require 128-bit encryption