Connection Closed Error

We have 3 integration servers sending xml simultaneously to another integration server’s Trading Networks using [url]http://localhost:5555/invoke/[/url] about 1000 times from each.
One of the three gives a Connection reset by peer: socket closed error and brings down the main server.
The main server is IS 4.6. We have tried connecting from 4.6 and 6.0 developers and got the error in both.
Any ideas? Thanks in advance.