Broken Pipe when receiving large files

we have a problem when we receive large files (about 35MB) using Reverse Invoke Proxy Server. (IS6.5 SP3)
In the server log of the Proxy Server i see this messages

[ISS.0080.0106D] Exception in SocketLink send:Broken pipe
[ISS.0080.0106D] Exception in SocketLink send:Socket closed
[ISS.0080.0106D] Exception in SocketLink send:Socket closed

I alredy adjusted this timeout settings at Proxy and IS :
Number of registered reverse connection to proxy : 8

But the problem still occurs…are the any more settings i can try to adjust ?
Would it make sense to increase the timeout and/or the numer of connections further ?

Thanks in advance