I need to change the default error pages that DNN uses - PLEASE DO NOT recommend setting up the error pages in IIS, I already know how to do that and that will not accomplish what I need.

Here's what I've determined so far: In the root of the website there is a ErrorPage.aspx and associated code behind (this is in 4.5.3 Source install as well as a non Source install)  I can go to that page and add some HTML to aspx. I can then reset IIS, and then before hitting the site, stop the database. When I hit the site the URL is changed from http://dotnetnukesource to http://dotnetnukesource/Install/UnderConstruction.htm (dotnetnukesource is the instance running on my dev machine with a host file entry).  That page displays an "Under construction message" - I then change the URL back to http://dotnetnukesource and try again. The second time I get the ErrorPage.aspx with my new HTML in it - and I see the Page_Load in the code behind fire while watching in the debugger.

I then turn the database back on and hit the site and the site come up normally. I then take the db back off line and hit the page again - this time I get a similar looking error page but the fonts are different AND my html isn't in there. While watching what happens in the debugger I don't see the page_load in the code behind firing either. It looks like there might be some code in the XMLLoggingProvider.db code that's returning the different version of the page, but I had to resinstall the solution - and now i can't reproduce the behaviour.   One other thing I've noticed is that there is no Application_Error Event handler in the global.asax located in the app_code directory of the website - can anybody comment as to WHY this isn't being used?

Any help would be appreciated.