System error 53 has occurred

For some time, we have been having problems with our remote clients accessing certain network resources over VPN connections. These problems occur when a client PC is connecting to our network over a Cisco VPN connection. They can perform some activities such as E-mail (MS Exchange server 2003 or 2010 and Outlook 2003/2007/2010 mail client), applications that use a Terminal Server connection, connecting to our Intranet web pages, and the ability to connect to the Netlogon folder on the DC. However, in the case of connecting to the Netlogon folder, when the BAT file runs to map their network drives, they receive the error message "System error 53 has occurred. The network path was not found." We have their My Documents path configured to use a FQDN path to "\\Domain\dfs\Department\UserName" where our domain name is used rather than a specific server name as there are several different file servers that house the different file shares for our departments. When they double-click their My Documents folder on the desktop, they get a message that the file or folder is not found.
Now for the strange part - this is not permanent, but usually only lasts for 10 - 30 minutes after they are connected to VPN. I just tested this at home, connected with VPN, and ran the BAT file to map my network drives. I ran the file every 30 seconds, and at 13 minutes, 30 seconds, the network drives finally mapped. We use Sophos AV (version 7.9), and had thought that it was the firewall piece of this software that may have been the problem. I completely removed all Sophos components from my PC, rebooted, and established my VPN connection. It did not help. In fact, this was when I got the 13:30 timeframe for my network drives to show up, so it isn't the Sophos. I have tried 2 different VPN clients, "Cisco VPN 5.0.04.03" and "Cisco AnyConnect VPN Client Version 2.5.6005". Each of these clients is configured to use its own Cisco VPN Concentrator back in our server room. The AnyConnect is our newest client/concentrator that we hoped would help in this problem, but I get the same results regardless of which VPN Client/Concentrator I use.