Screen flickers badly when using KVM switch and an external monitor

Hi

I'm trying to use a Macbook pro with a 2 port KVM switch and a 24" Cibox monitor with a 1680x1050 res and a 60hz refresh rate. When I plug the monitor straight into the laptop everything is fine. The problem is when I link the monitor via the KVM switch the screen flickers like crazy and when I alter the settings on the laptop it says 'out of range'. Any ideas on what the problem might be and how I can solve it?

Thanks