1. Empty cache and then refresh page should fix the problem. Or simply hit Ctrl+ Shift+R in FF or Ctrl+F5 in IE should updated the page with the latest server contents.
2. You are probably editing the wrong file. Can happen if the same project exists in two different location. Your editing in a wrong project and not seeing the results!
3. The IIS server is pointing to the wrong project. You recently or a while ago moved the code and changed the IIS directory but you forgot to update the project directory for this project.
The above should hopefully resolve your problem. In my case it was #3 that was causing the problem.
The above solution should work if you are looking for
Code Changes not taking effect
ASP.NET code change does not take effect