Visual Studio detaches from application as soon as debugging starts

Question

I have a web application that I've always been able to run in Visual Studio and it debugs just fine (breakpoints work, I can pause execution, etc). Recently, the behavior changed suddenly, and a few things happen:

• I start debugging, it lauches IE and loads the application, but after a few seconds (sometimes the page hasn't even displayed yet), Visual Studio acts as if debugging has stopped - I'm able to edit code in VS again, and the "Play" button on the toolbar is enabled. The application continues to run in the IE window just spawned, but I'm not attached to it
• During this few seconds that VS is "debugging", because it detaches, my breakpoints show as hollow - as if I'm set to "Release" mode and they won't be hit. In fact, I have a breakpoint set in Page_Load, and it skips right by. I've checked, and I'm set to debug mode, though the compile mode dropdown is missing from my toolbar (I checked in the build properties to ensure I was in debug mode).

Can anybody shed some light here?

Answer 1

It turns out that this was actually a result of an upgrade to Windows Vista. VS wasn't being "Run as an Administrator", which caused it to lack the rights to attach to other processes for debugging. As a result, debugging would stop right after it started. Changing the VS shortcut to run as an administrator resolved this problem.

Answer 2

I've experienced samely looking behavior. The cause was in existence of several <system.web> sections (which is allowed by web.config schema). Visual Studio debugger (versions 2008 and 2010 were tested) looks in the first encountered section only. So if your <compilation debug="true"> tag is not in the first one, it thinks that there are no compilation.debug setting present and genrally tryes to add <compilation debug="true"> to the first <system.web>. In some cases VS2008 just silently procceds in this case. For example look here: https://connect.microsoft.com/VisualStudio/feedback/ViewFeedback.aspx?FeedbackID=510354#details"

Answer 3

Have you installed anything else on the server / workstation recently?

We have a third party app that doesn't allow us to debug, w3wp.exe crashes immediately upon an attempt to debug.

Answer 4

I ran into something similar when I had placed some code in a constructor that was crashing. Exact same issues where the Debug would disconnect just after the application started up.

The short if it, check that you haven't configured a class constructor to run during web startup that is crashing...

Answer 5

Quick windows 7 update: I had to add "localhost" to my list of trusted sites to correct this issue...go figure.

Answer 6

Just a workaround for those (like me) for whom the above solutions do not work: After starting the app you wish to debug, go to Debug -> Attach to Process, and attach it to the process you want to debug. Works on my machine.