My debugger won't work!

I have a small .net application that I help maintain from time to time, and I needed to drag out the old debugger the other day to help someone out. For the life of me, I could not get the debugger to stop on breakpoints in that project. I tried a VS2005, 2008 and they both had the same issue. I checked the obvious 'turn on debugging' web.config setting several times. I scoured the interweb looking for help. Most of the references I found to this type of issue were times where the .pdb files were not getting recompiled with code changes, and the IDE would give you warnings to that effect. In my case everything seemed perfect. No warnings at all. It just wouldn't stop at the breakpoints. Frustrating!

I finally came across a microsoft article on debugging that pointed me in the right direction. Did you know that there's another 'turn on debugging' setting for your application? I'm not really sure what it's purpose is, but there's another checkbox that turns on debugging buried under the 'start options' dialog. Really intuitive. Here's a screenshot:

If anyone has information on what the point of that checkbox is (compared to the one that controls the setting in web.config), let me know!