I don't think I'd blame it on OneCare, though you can try the following:
1. Turn off the OneCare firewall temporarily via Change Settings, firewall tab. If it works, yes the firewall would be the culprit.
2. Reset the IE settings to default - Tools/Internet Options/Advanced/Reset button
OneCare wouldn't block a specific function, which is why I doubt that it is OneCare. It may be a broken control in IE or a security setting in IE that was shifted.
-steve