It seems that since v. 240 you have add'd the possible to request a page without .aspx extention which is great. However there's an bug there. If you reuqest an page without .aspx with eigther ø or æ or å , it will not add .aspx in your rewritepath code.
I temporarely fixed this by adding the following code in global.asax.cs under Application_BeginRequest
strURLLowerede = Server.UrlDecode(Request.RawUrl.ToLower());
if (strURLLowerede.Contains("ø") || strURLLowerede.Contains("æ") || strURLLowerede.Contains("å"))
{
if(!strURL.EndsWith(".aspx"))
Context.RewritePath(strURL + ".aspx");
}