Thank you for the reply. Having now tried three versions of PHSNA ( one unknown, V1.39 and 1.40) I now realise that Windows sees them all as V220.127.116.11!. But anyway they each produce exactly the same error message.
Yes I meant that I don't have Excel. Both Kingsoft Office and Open Office are just to difficult to get sense out of (for me!), but I have been able to produce graphical results in my "usual" spreadsheet - "As Easy As".
I was hoping that the Windows software would be instant enough to allow live tweaking of a circuit, but although the spreadsheet path takes a long time it is infinitely better than signal generator + rf meter + pencil and paper!