And it disappeared in the same way. When I logged on this morning it was there, and I had to again tell my computer to ignore it. I did nothing to remove it. When I came back to the site later, and logged on again, the certificate was gone, and log on was as normal. This evening I logged on using the spare computer, and found the certificate here too. I ignored it, read the site, and logged off. Just a little later I logged back on, and the certificate was gone. I was able to log on normally.

This may be one of life's little mysteries.

Thanks for your help.