I have Microsoft Visual Studio Professional 2012 installed, version 11.0.60610.01 Update 3.
When debugging a c# (.cs) file Visual Studio gives me the following message when I try to set a breakpoint:
"A breakpoint could not be inserted at this location".
I was finally able to find a solution for this. I had to do a repair on my Visual Studio 2012 instance through the control panel -> Programs and Features, right clicking on Microsoft Visual Studio Professional 2012, and selecting change. In the Visual Studio window I then selected repair.
As part of the repair process, I also had to download web deploy located here: http://www.microsoft.com/en-us/download/details.aspx?id=4148 and point the visual studio repair process to the .msi file when it said it couldn't find the web deploy package and could not download it from the internet.
I also had to implement the fix indicated in the following stackoverflow question: Plain C# Editor in Visual Studio 2012 (No intellisense, no indentation, no code highlighting)
Now I am able to debug applications as expected.