I booted into Windows 7 today after not using it for a while, and I saw "some network drives were unavailable" in the corner of my screen. I disconnected the drives, and used map network drive to add a new one. It sees the server, but when I get to "Enter Network Password" every username/password combination results in "Logon failure: Unknown user name or bad password." There are only 2 user names and passwords that are used on my various computers in the house, and no combination of them worked. What's really strange is that the mac server is set for everyone to have read and write privileges.
This is very irritating... I'm usually good at troubleshooting these things but I'm absolutely stumped.
The password it wants is probably the one the system created and invited you to save somewhere when the Homegroup automatically set itself up. Go into Control Panel>Network and Sharing Centre and come out of the Homegroup and stick to conventional networking. Also, untick the requirement for password protecting networking so long as you're sure of your network security.
That should do the trick but please post back if it fails to.