OK, this one has had me scratching head. Next option is look what is happening over the NIC with wireshark etc. but for now any bright ideas, sorry for the long details but imagine most initial thoughts would be things already tried otherwise?
"old" situation. XP machine, transferring files to NT4 server. This has special transfer software to an ancient piece of CNC equipment so for the time being isn't changing, though I may virtualise it if it stays much longer. Transfer rates from here are fine, think they were in the order of 800Kbytes a second, haven't looked yet but assume the NT4 box has a 10Mbit card.
So the XP machine is moved to a new location in the plant, same transfer, fine.
It is plugged into a small 5 port 10/100 switch as there is only one cable coming into that office. In that switch there is also now a Windows 7 machine. Same software, drive mapping etc. It can READ from that share at the same sort of rate 800Kb/sec but writing to it is next to a crawl, i.e. a 15Mb file is predicted around the 3+ hours mark, something like 1Kb/sec, no it isn't connected via 9600 serial cable!
Connected my Win 7 laptop to the same switch, gave it relevent IP address range and same transfer speed issues.
There is no anti-virus, firewall or other software in the way here. NIC is on latest drivers etc. and all on "Auto" for duplex etc. Binding order correct, IPv6 off.
Changing NIC to 100/full fixed brings the transfer speed up to 30Kb/sec but the full line speed comms to other servers then drops to 300Kb/sec from 4.5Mb/sec or so like a duplex mismatch issue. Other NIC settings don't make any real difference including flow control etc.
Now... Windows XP mode Virtual PC installed on that same machine will happily transfer through the same NIC and network at the full 800Kb.sec again.
So that pretty well rules out NIC, cable, switch, server leaving Windows 7 handling of file transfers to NT4?
Most internet searches etc. come back with the normal issues of duplex mis-match etc. Are there any parameters that you think may help?