This may be caused by a security zone setting - "Allow scripting of Internet
Explorer web browser control".
The safe way to do this would be to enable this setting for the Trusted
Sites zone and then add those sites that you trust to the zone so that your
form-filling software can work.
What software are you using BTW. The Google and Live Toolbars come with form
filling functions and RoboForm, I find is quite good, although my personal
recommendations is not to use any toolbars or browser extensions.