Hi,
Building manually simply means to rebuild your code from within Visual Studio itself. Usually, a common fix to most of the sudden VS issues is to regenerate and rebuild the solution. Please refer to this answer where I explain how to do this.
I just saw someone had his issue with VS resolved by installing “NuGet package manager” (AnswerHub post). Though I myself never faced such problem, it might be the cause of your issue!
Hope this helps.