How to get the physical location of an ASP.NET web application without using HttpContext.Current?

I’ve found myself having a requirement to configure log4net based on a file relative to the physical location of the running ASP.NET web application. We like to start the logger as early as possible, so Application_Start seems a proper place. In IIS6, this works fine and has been running for ages, but now we moved to IIS7 and this won’t work anymore:

Why won’t my form post back after validation?

I have an asp.net page with multiple validation summaries setup with ShowMessageBox="True" and several validators. I have run into a situation where when validation fails the validation summary displays correctly but then the next click that would normally trigger a postback of the page does not trigger a postback. So the steps look like this: