HI Bill,

have had the same problem than you just after install.
In DNN, Tools, Clear Cache and  Restart Application Pool.
In your navigator, Clear cache and cookie
Relog, you might be able to load an Extension.

HTH

I ran into this same issue which affects not only the Extension Install Wizard but also most other file upload controls which make use of a hidden html file element (input element of type="file") when using Internet Explorer only. For example the various logo and other image upload controls on the Site Settings page.

Apparently it is a known issue (or perhaps security by design) in IE 8 + that anytime an html file element is hidden a subsequent postback of the page will be blocked with the Javascript error "Access Denied".

In DNN 7's dnn.jquery.js script the function fn.dnnFileInput is applied to all html file input elements on a page to provide a highly stylized control. In so doing the file input element is hidden with the inline style="display:none" being applied. It also appears that the text "Choose File" of the link button that is shown instead of the usual "Browse" is not localized but rather hard-coded in this function.

I'll check Gemini and add this as a support issue if not already entered.