You're welcome, replies are what we do here, however; actual answers and solutions might be a different story.
Does this problem happen regardless of the
file(s) size?
number of files you are attempting to transfer at any given time?
Have you ran chkdsk /R on the external drive?
Have you recently defragged both the source drive and destination drive?
Can we assume that your Windows 7 install is up to date? (service packs, updates, patches and hotfixes) since this was reported as a pretty prevalent problem early on but I thought that MS had addressed it with a hotfix.
See if the problem persists if you boot the machine into
safe mode
EDIT: Also forgot to ask, does the type of file seem to have any impact on the issue. In other words a single or couple .mov or .avi files as compared to a folder full of .txt files?