If you copy files over a slow WAN link and get the message "Cannot complete input operation," your session probably timed out. To increase the amount of time NetBIOS allows before timing out, you can apply the following Windows NT registry hack :

Hive: HKEY_LOCAL_MACHINE
Key: SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameter
Name: SESSTIMEOUT
Type: REG_DWORD
Value: 45 default, 10-65,535

Q98849- Adjust Parameters to Connect to LAN Man Over Slow Link

With a domain spanning into multiple sites, NetBIOS name resolution mode should be set to m-node ( broadcasts followed by name server) on all servers and workstations. Forces a local domain controller to be contacted first, before trying to contact the PDC (which is probably not local).
Hive: HKEY_LOCAL_MACHINE
Key: SYSTEM\CurrentControlSet\Services\NetBt\Parameter
Name: NodeType
Type: REG_DWORD
Value: 4 M-NODE