http://stackoverflow.com/questions/2155930/fixing-the-breakpoint-will-not-currently-be-hit-no-symbols-have-been-loaded-fo
unable to hit the breakpoint
Start debugging, as soon as you‘ve arrived at a breakpoint or used Debug > Break All, use Debug > Windows > Modules. You‘ll see a list of all the assemblies that are loaded into the process. Locate the one you want to get debug info for. Right-click it and select Symbol Load Information. You‘ll get a dialog that lists all the directories where it looked for the .pdb file for the assembly. Verify that list against the actual .pdb location. Make sure it doesn‘t find an old one.
In normal projects, the assembly and its .pdb file should always have been copied by the IDE into the same folder as your .exe. The bin\Debug folder of your project. Make sure you remove one from the GAC if you‘ve been playing with it.
需要去确认下项目的生成路径，清空路径下的pdb文件。
清理解决方案的时候，有可能没有清理干净。