fs-cifs communicates by telegraph

Some days ago I complained about that the backup I make on an NT server
are very very long to do.
This morning, I’m copying a 520 Mb file. The ‘File Operations’
dialog box give me an estimation of 9:23 hours !?!

On the qrtp platform:
The network load is actually about 5% (Tx: 37 kb/s Rx: 27 kb/s) with
some peaks to 19%.
The cpu load average is 8%.

On the NT server:
The network load is about 0%
The cpu load is 1%

What’s the problem?