So I’ve been hearing a lot of folks (myself included) having issue with debugging there web application with VS 2010, Cassini (the VS web server) and IE9. It looks like this Well I found and easy solution, image that . Edit your hosts file at location c:\windows\system32\drivers... and make sure the localhost 127.0.0.1 line is uncommented and the localhost ::1 is commented or deleted. You can ping locahost host from a command line and make sure you see Reply from 127.0.0.1: bytes=32 time<1ms...