Hi Bart Welch,
Generally the page should be opened in the iframe window. Most probably you have some code on this page that somehow breaks the backend. You could try
1. Remove the logic from the external page, so that this should allow you to edit it.
2. Remove the page from sitefinity using the code below:
var Manager =
IList allpages = Manager.GetPages();
(p.PageType == CmsPageType.External)
ICmsPage removePage = (ICmsPage)Manager.GetPage(p.ID,
"the external page has been deleted"
"there is no page with this name"
All the best,
the Telerik team