With VS 2008 this is an odd thing that just in time debugger keeps popping up when you have javascript url set with a script tag on the page.
For example

I find it very annoying as it keeps popping up while i try to type in code!

Setting from VS 2008 > Tools > Debugging > Just-In-Time simply doesnt work.

Without going for why it happens, this is how you can get rid of it.

* Click on start menu
* Click on Run if you are using XP. On vista or 7 you can use the search box.
* Type regedit
* Hit enter button
* Expand HKEY_CURRENT_USER
* Expand Software
* Expand Microsoft
* Expand Windows Script
* Double Click on Settings
* Double Click on JITDebug
* Set 0 for “Value Data”. Click on Ok
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From Webcosmo Webmaster Forum http://www.webcosmoforums.com/asp/26385-just-time-debugger-keeps-popping-up-visual-studio-2008-a.html