No error messages in classic asp in IIS7

When my classic-asp pages encounter an error the execution of the page
is stopped (which is normal). However, the error message is never sent
to the browser. Everything outputed before the error is sent.

If I put something like

Response.Write "Dummy output"
Response.End

after the error, the error message will be sent to the browser.

I have unchecked the "show friendly http error messages" in IE and I
have tried a lot of different settings in the IIS-manager (like use/
don't use custom error messages, send error messages to browser etc).
But nothing seems to solver the problem. Any ideas?