Have you figured this out yet? If not I DO know the solution :)
There is a setting in windows Local Security Policy which is incorrectly set by default for viewing an older communication protocol NAS.
To access said setting go to the control panel in Windows 7, in Category view click on the text "System and Security", then click on the text "Administrative Tools".
Now double click and open "Local Security Policy".
In the Local Security Policy screen on the left navigation tree, expand the "Local Policies --> Security Options" then about 2/3rd's the way down the list you'll see a Policy called "Network Security: LAN Manager authentication level". Double click and change the setting to be "Send LM & NTLM - use NTLMv2 session security if negotiated."
Then just press OK and close all of the open windows and then try again :) it should work.
BUFFALO TECH: Please put this in your documentation someplace because it took me forever to find this.
Thanks!