..The underlying connection was closed: An unexpected error occurred on a receive

Here's a good thread of things to try:

http://social.msdn.microsoft.com/Forums/en/ncl/thread/47634ec2-4d40-4d3f-b075-8cc92bfa2b24

Increasing the timeout is probably a good idea in the least.

Just want to strengthen ScottE's diagnosis, and be more specific. Timeout is most likely the issue.

Either .Net implementation of FtpWebRequest is erroneous or the MSDN document has a typo, the default value of FtpWebRequest.Timeout is not -1 (Infinite). It is 100000 (100 seconds).

In addition there is another timeout issue. A few tests have shown that responseStream always has a timeout value of 300000 (300 seconds). I do not know how this value is assigned. Anyways, this value needs to be modified to accommodate large files.

In summary, the solution is to set FtpWebRequest.Timeout and Stream.Timeout to a sufficiently large value.