Multiple Application_Start events firing

Question

I am debugging an ASP.NET 2.0 application that is suffering from slow loading of the initial page.

Through adding logging, I've found that the Application_Start event fires twice on startup with a short delay between the two events. The Session_Start event also fires twice, with the same Session ID value.

e.g.

[Header]
2010-09-10 14:52:36.331 INFO  Web.Global.Application_Start          START
2010-09-10 14:52:37.409 INFO  Web.Global.Session_Start              Session.SessionID=xxqjvun2ce2yqsumq1hfoj45
[Header]
2010-09-10 14:53:10.028 INFO  Web.Global.Application_Start          START
2010-09-10 14:53:10.325 INFO  Web.Global.Session_Start              Session.SessionID=xxqjvun2ce2yqsumq1hfoj45

I am running this on my local machine, under IIS 5.1. The project also uses ASP.NET MVC and the aspx page URL being used is altered using routing, using the technique shown on Phil Haack's site.

Any suggestions about what could cause this?