I didn't make it!
I've downloaded some maps for cod2 from this site to spice up the lan parties I'm having in the neigbourhood.
First I downloaded 3 maps, just to try out if they would work, and sure enough they worked, no problems, the servers started, and the gameplay was the same. Then I got some more new maps, but when I copied them to the computers I started getting the message "iwd sum/name mismatch" when I tryed to start a mp game. Not only on the new maps, but even on the default ones, the server wouldn't load with that message appearing. On the computers without the second load of new maps everything worked ok.
Since the only difference between working and not working is just the copying of the map files, I don't know what the problem is..
Any suggestions/solutions anyone?
*edit* whoops, found that some ppl already asked basically the same question. So I'll try to turn pure server off the next time we have a lan party.. I don't even remember that option is in the game.. :)