Are you downloading many files at the same time? How big are the files?
Can you set the TraceWriter property so we can get a log of the communication with the server?
FtpClient.TraceWriter = new StreamWriter( @"D:\ftp.log", true );
I suggest you do it both when debugging and at runtime, to see if there is a different.
You can post the logs here.
André
Software Developer and Tech Support
Xceed Software Inc.