Again, thank you everybody for your interest in my situation; I’m really grateful.

In answer to ADY4UM,I’m using AVAST Paid-for Internet Security. It’s been running without problems since I installed it in mid-September this year. This followed on from a month’s free trial - very satisfactory.

I note that another correspondent, Sitka Larry, is having the same problem now, with Windows Vista 64-bit. Could that mean that the difficulty arises at AVAST’s HQ???

I await the results of your collective wisdom - thanks a lot!