"Ionic could not be found" error when building unrealbuildtool

I tried to build the projects source one by one manually according to their dependency relations. First, the DotNetUtilities builds successfully. But when I try to build UnrealBuildTool (right click the project and click ‘build’) I get this error:

It says something wrong with namespace ‘ionic’. I checked online and found ‘ionic’ is related to DotNetUtilities. Did I miss something? Or I simply cannot build the projects one after another this way? But since ‘UE4’ depends on ‘UBT’, and ‘UBT’ depends on ‘DotNetU’, isn’t this the same process as when building ‘UE4’ directly?