I tried to reproduce your issue, but I had no problems to embed and show the course catalog page (http://vanguard.360training.com?state=3&vertical=1&page_view=2) in an IFrame module on my development server.
I tried IE 6/7 and Firefox, in edit and view mode, but the embedded page always showed up. I used the latest IFrame module, version 4.3.0, in DNN 4.8.0, with the default module settings. So I can only guess what the reason for your problem could be:
- Make sure that you run the latest IFrame module version
- If you changed the module settings, try it with the default values
- Try to view the page fom another computer outside your company network
If that doesn't help, you should post your issue again in the DNN IFrame forum. Thats where the IFrame experts are :-)
BTW: I noticed there's a login on the embedded page. If that page stores the login data as cookies, then the users must have third party cookies enabled in their IE to make the login work; see thread "Login in Iframe not working".
Good luck!