Make sure you are changing the ActiveX settings to always or prompt under trusted sites zone. Also make sure when they are going to the site that it is in the trusted sites zone (at the bottom of the browser) in the status bar.
Also make sure they are administrators on their boxes.
One last thing to check is make sure the activex is not still in there. I only have IE8 installed and it is under Programs->Manage Add ons. I think it is very similar in IE7.