What software are you using for proxy scanning? You might need to adjust some of the settings in that software.In particular if there is an option of entering "Delay between each packet".For example,if i am using SuperScan 4.0 to do a scan,the delay is set at 10ms.If i was to lower it beyond that,my connection drops out also.I have had similar experiences with other port scanners also.So do some trial and error with your settings until you find a combination that won't cause your internet connection to drop.