IE 8 has a feature called Loosely-Coupled Internet Explorer (LCIE) which results in IE running across multiple processes. http://www.microsoft.com/windows/internet-explorer/beta/readiness/developers-existing.aspx#lcie Older versions of the Visual Studio Debugger get confused by this and cannot figure out how to attach to the correct process. You can work around this by disabling the process growth feature of LCIE. Here's how: 1) Open RegEdit 2) Browse to HKEY_LOCALMACHINE -> SOFTWARE -> Microsoft -> Internet Explorer -> Main 3) Add a dword under this key called TabProcGrowth 4) Set TabProcGrowth to 0