This requires that you change the lanman server parimeters in order to get Windows 7 working with older servers. Do these adjustments on the Windows 7 machines that need to connect to the server.
I'm not sure if this has to do with your exact problem but these adjustments are usually required to get Windows 7 working with older servers.
Control Panel - Administrative Tools - Local Security Policy
Local Policies - Security Options
Network security: LAN Manager authentication level
Set to Send LM & NTLM responses only
Set the Minimum session security for NTLM SSP
Disable Require 128-bit encryption
The screen shots below should be helpful.
Reboot all machines after making the adjustment.