I have been having this problem for months now... every time I attempt transfer a large amount of data between my computers, one or both of the machines lose their network connection and windows does the "Default Gateway is not available thing"

I have looked online and tried all the fixes,

Updated network drivers on both machines to latest available, Re-installed windows
Replaced network cables,
Replaced router,
Even tried different network cards

Problem persists no matter what I do...

Is this a fault in windows or am I missing something?