Target “build” does not exist in the project for Visual Studio

The accepted answer is a workaround, not a solution. You need to open the .csproj file for editing in a text editor and ensure the following line is present in there

<Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />

If not add it to the end.

Note: For VS2008, this may be $(MSBuildToolsPath)