I was having this issue for several days. I finally figured out a fix for ASP.NET programmers, and I figured I would share.
After setting a breakpoint, and then debugging my breakpoint would turn yellow with an exclamation point. When hovering over the breakpoint it would say "The breakpoint will not currently be hit. No symbols have been loaded for this document.”. I tried cleaning, rebuilding, changing various settings through my project and visual studio. Nothing worked.
I was digging around in the Solution settings. I noticed that under "Web" tab my
Start Action setting was set to something other than "Current Page". After setting it back to current page everything worked out.
I hope this solves the issue for other's like me that were exhausted after trying every other suggestion/answer they could find on the internet.