Network windows 7 and OS X

Goto Start Menu
Search for: security
Click on Local Security Policy
Goto Local Policies> Security Options
Double Click on Network security: LAN Manager Authentication

Look in Network for the OS X computer you have enabled sharing on !
Change level to: Send LM # LTLM Responses

Then, scroll down to Network security: Minimum session security for NTLM SSP
De-select Require 128-bit encryption
Hit OK