Refer to class-cannot-find-another-class-in-the-same-namespace Ensure that the files in the v2 folder have their Build Action correctly set to Compile:

• In Solution Explorer, select the files in the v2 folder, right-click, and choose Properties.
• In the Properties window, ensure that the Build Action is set to Compile.

Remember close VS2017 down, reopening, Clean and Rebuild the project after setting Build Action