Error: Schema validation failed with the following errors: Data path "" should NOT have additional properties(project)

The issue is generally because of a version mismatch in your package.json file.

In my Angular 7 app, I have changed "@angular-devkit/build-angular": "^0.800.2" to "@angular-devkit/build-angular": "~0.7.0".

Then I ran the command npm install after deleting node_modules.

Aside: Use ^ carefully. Your working code may not work in the future if there is a major change in the package used.

my app is on angular 7.2.3

remove "es5BrowserSupport": true from angular.json. and npm start now works.

When i was getting version error issues,Following command worked for me:

First run:

npm update

Second run:

ng update

Third run: (It will update all the mismatching packages)

ng update --all --force