Javascript not working in IE6 under certain AD accounts

I am in a WinXP company environment in which JavaScript is not working in
Internet Explorer 6 under certain AD accounts. This started happening
around a week ago.

At first, we thought JavaScript stopped working on the PCs themselves, but
found that if certain other users logged in, JavaScript was working again.
The problem is associated with specific AD accounts, not with the computers
themselves. All the users here, whether or not they are having this issue,
are under the same OU.

These are all Windows XP Pro machines. On a couple of the desktops, while
one of the problem AD accounts was logged in, we checked IE6 custom
security settings to make sure JavaScript was enabled, It was ... 'Active
scriptng' and 'Allow paste operations via script' and 'Scripting of Java
applets' were all already enabled.

Uninstalling and reintalling JRE made no difference, which we expected
since the problem is with JavaScript, not Java.

We ran 'gpupdate /force' for each of these problem accounts, but it made no
difference.

Any thoughts on what could be going on? TIA