Question: I have a Visual Studio 2010 solution with a few projects. I can successfully build with Build -> Build Solution or Build -> Build MyCompany.MyProduct.MyProject. After building I press CTRL+F5 and successfully run the start up project. This works as expected.

After I change a source file, save it and then again build (with either Build -> Build Solution or Build -> Build MyCompany.MyProduct.MyProject) it builds successfully. I am still able to press CTRL+F5 and run the startup project. This again works as expected.

The problem is in the following scenario:
After I change a source file, save it and directly press CTRL+F5 then Visual Studio 2010 says BUILD FAILED and there are no errors. And it doesn't start my startup project (of course).

Am I missing something?

Answer: 
Check your project physical path , If is to long , Copy project to some root directory folder with very short name.
And try to build your project.
Has this issue when dealing with Sharepoint 2013 Workflows in VS 2013. To solve it did the following:

1. Unload worklfows ( the buggy one) project.
2. Delete .csproj.user file
3. Opened .csproj file in the notepad and delete the following lines:

```
 <PropertyGroup>
  <VisualStudioVersion Condition="'$(VisualStudioVersion)' == '' or '$(VisualStudioVersion)' &lt; '11.0'">11.0</VisualStudioVersion>
 <VSToolsPath Condition="'$(VSToolsPath)' == ''">$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)</VSToolsPath>

```

After RELOADING project into solution, the VS added exactly the same lines AGAIN, but no LoaderException issues now.