Turbo, you mean the "Manage Attachments" button on the reply page, right? I just checked my IE settings to confirm what I suspected, your IE is blocking the attachments pop-up - I got the same thing when I changed my pop-up blocker from "medium" to "high".
Go to Tools> Internet Options,
choose the Privacy tab,
here you'll see "pop up blocker" click Settings,
now you can either set your level to medium or add "forums.sirstevesguide.com" (minus the quotes, naturally) to the list of allowed sites.
When finished, click "close".
That should take care of it, LMK if it works or not.