Thanks GlenAustralia, but as others have commented, the "culprit" is not Nokia Suite (which I don't use), nor is it ZoneAlarm (which I do), nor is it ANY other third-party app - the culprit is Microsoft Excel itself.
If running two completely separate dedicated PCs - one especially for Nokia Suite and one especially for Excel - seems an acceptable resolution for you, then so be it.
But personally I think that's a bit much to ask of each and every Excel user - and there appear to be many - who's afflicted by this issue, which MS has had several YEARS to reply to and resolve, and which they pointedly have failed to do either.
I don't mean to bemoan MS in a general sense - personally I have found their tech support in other areas to be first-class - but in this particular instance, it can't be denied that it's been simply appalling (in the sense of being non-existent).