E6420 and Linkskey KVM dual monitor issue - second monitor flashes randomly

I have an E6420 in an E-dock, connected to a 2-port Linkskey KVM LDV-DM702AUSK, the other PC is an XPS-420.

Windows 7 on both machines

Everything works fine on the XPS 420, switching to that PC, both monitors work in extended display, keyboard, mouse - no problems.

When switching to the E6420, the second monitor (Dell 2208WFP) will start to flash after a time, as if the PC suddenly loses contact with the monitor, but quickly re-establishes and my display is OK again.  This process increases in frequency at times, until it is off more than on, and impossible to work with.  The only solution I have found so far is to disconnect and reconnect the video cable - but this does not fix anything for long.

The 2208WFP is connected via DVI, my primary display is a Dell 1905FP, which is directly connected by VGA from the E-Port.  I have to manually switch the 1905FP monitor from machine to machine because of the VGA / DVI mismatch on the KVM.

The XPS-420 machine uses DVI to the KVM for both monitors, and as I said, works great.

I have looked for any suggestions, driver changes, display mode changes, etc. and nothing is working.  Please help!

(Current display on E6420 is32 bit color depth on both displays,  1280x1024, 60Hz on the 1905FP, 1680x1050 60Hz on the 2208WFP monitor - have also tried 59Hz without changing anything).

Thanks!

Tom