Try using ROBOCOPY instead of using regular copy or xcopy.
I have seen Windows 7 hang because of the extra overhead when using the "graphical" copy.
Or, if you are unsure of what is blocking, you can try HOBOCOPY. That's not a typo. It's almost exactly like Robocopy except it will allow you to copy files even if they are in use.
Both are command line and should not be affected from SEP.
Robocopy is built into System32 on Windows 7.