If you get this error, it must be in the logs. Please double check if you are looking at the correct logs.
While using .NET assembly I get this errors periodically. But the Session Log file doesn't seem to have errors.
Transfer channel can't be opened. Reason: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
Copying files to remote side failed.
Data channel timed out.
Many thanks ;)