If you receive a pop-up message, Cannot complete input operation, when copying files over a slow link, it is probable that your session has timed out.
You can increase the the amount of time that NetBIOS uses before timing out by editing:
Double click on SESSTIMEOUT and set this REG_DWORD value to a decimal number between 10 and 65,535. The default is 45 seconds.
Windows NT uses a dynamic SMB response timer algorithm. The redirector determines the bytes per second rate and calculates how long the transfer should take. It adds this to SESSTIMEOUT which you can think of as a safety factor.