Mime type error message while accessing mobile web application

[Remco]

I am having troubles accessing an asp.net mobile web application.
When I run the page on my wap-enabled mobile phone (or with an wap emulator
like www.wapsilon.com), I get an error message saying:
Wrong mime-type, I got text/html; charset=utf-8, but I want
text/vnd.wap.wml.

When I make an simple .asp file (with Response.ContentType =
"text/vnd.wap.wml" in the very top of the page), instead of an aspx file
,everything runs fine.
I have created the application with VS.NET 2003, via File -> new project ->
mobile web application.

I am running IIS 5.0 on the webserver, which is a windows 2000 server.

Any help would greatly appeciated.

Remco