I've not been able to play Killing Floor online since it was released, this was a pain, but I took it on the chin. When I updated to Windows 7 I decided to look to see if my problem was resolved, turns out it wasn't, however I did find the reconnect solution, and it works!
I use a BT Home Hub - and while it is annoying that my router is the cause of the problem I totally undertand that this is really out of your control. You can't test every type of router on every type of PC, it would be impossible. This is espically true when said routers are not even avaiable worldwide, or even in the country of origin!
I am glad to hear that Thompson have replied, thankfully for me the reconnect command seems to work perfectly, and I accidently lost the last 3 hours in Killing Floor - for the first time since its release.
Good luck on a solution, and I wish everyone who cannot connect to KF a speedy resolution!