I think this is probably exactly what you’re wanting:
http://blogs.msdn.com/b/zainnab/archive/2010/05/16/hide-or-show-error-list-when-the-build-finishes-with-errors-vstiptool0022.aspx
You can change this behavior by going to Tools -> Options -> Projects
and Solutions -> General and deselecting the “Always show Error List
if build finishes with errors”.
I’m guessing this will work with ASP.Net as well, since that’s building on the fly.