Borg and Mikey - many thanks for the info.
I did more testing and can confirm that when using IE on a workstation it all works fine when I switch off "Scriptscan" under VirusScan on-access properties.
However, when using IE on the server the results are not so definate. It seems to be connected with this option although results are inconsistent. Maybe this is what Mikey is seeing.
Ignoring the server, the problem affects all forum members who use VirusScan with its default settings. They are unable to edit their posts and perhaps there are other restrictions brought about by script blocking that we should make them aware of?
A lot of people use VirusScan. Should they all switch off this security feature, do without editing their posts or could a forum software change solve the problem?
My preferred workaround for now is to switch off the security option only temporarily when I wish to edit.