Because of the changes in Windows security, many users experience common problems after upgrading to Windows Vista.  One of the common problems is the inability to map network shares to existing NAS (Network Attached Storage) devices.  A common symptom of this issue is the error message "Failed to map drive” when attempting to map a network share.

Many NAS devices do not currently support the NTLMv2 authentication enforced by default in Windows Vista.  To resolve this problem, you will need to enable the Windows XP style of authentication by following these steps:

1. Click on the Windows Start button and select Run
2. Type secpol.msc and press Enter
3. In left frame, under Security Settings, double-click on Local Policies
4. Under Local Policies, click on Security Options
5. Look for "Network Security: LAN Manager authentication level" in the right pane and double-click on it
6. In the dropdown selection for authentication level, select "Send LM & NTLM - use NTLMv2 session security if negotiated"
7. Close any open explorer windows and try to re-map to your NAS shares.

You should now be able to map network shares without any issue.