As I suggested in a similar thread (https://forums.factorio.com/viewtopic.php?f=49&t=62215)
Actually the easiest way is to just use the .zip download from https://www.factorio.com/download and make a factorio install that is separate your existing factorio installation. The .zip version will be ...

I still get the error msg:
could not move file "factorio-current.log" Another instance of factorio is probably already running
any ideas?

I made a config-server.ini file and changed it like this:
write-data=C:\Program Files\Factorio\server

I made a server.bat file and wrote
start /wait Factorio ...

My friend is getting horribly low download speeds when he is downloading the multiplayer map. Below 10kb/s. My upload speed is around 7Mbps so that should not be the problem.

What can I do to increase the speed or get around downloading the map when connecting?