''<p>Toad-Hall [[#answer-1512232|said]]</p>'' <blockquote>re :Antivirus is Avast free - I have not installed its firewall option. Info at link below: ''Although it is generally not recommended, you may want to exclude certain files, folders, or websites from being scanned by Avast Antivirus. '' ''Add an exception'' ''Setting a global exception will exclude individual files, folders, or websites from all scans and shields.'' '''Add as exception: 'aus.thunderbird.net' and also 'www.thunderbird.net' use info at link:''' * https://support.avast.com/en-ww/article/Antivirus-scan-exclusions Whilst this might not be an immediate fix on the machine running current version as you'll have to wait for update. When the next update comes through see if this gets added to the history. However, if you have Avast on the other computer which is still on version 91.3.2, see if adding the exception gets it to work and update. </blockquote> This seems to have done the trick. No more popup nag since I added the two exceptions. Thanks to everyone who chimed in.