Errors began after updating to Angular-Cli V10.1.0.

Initial problems I encountered:

• The ng command was not working. I found that core dependencies were missing: npm WARN @angular/fire@6.0.0 requires a peer of @angular/common@^9.0.0 but none is installed. You must install peer dependencies yourself.

I Tried:

• Installing dependencies manually.
• Uninstalling the angular-cli globally, clearing the cache with --force, rebooting and reinstalling.
• Downloading latest NodeJs, updating npm usingnpm update as well as Angular: ng update.
• Deleting: package.lock.json ; package.json ; node_modules

I could not delete node_modules:

• A folder: .xml2js.DELETE has a package.json file that can't be opened in my IDE or by Windows.
• I believe it's this file that's preventing me from running npm install

EUREKA - Problem Solved!

Steps I took which fixed the issue:

• Open Powershell as administrator
• Run chkdsk /f
• Delete node_modules
• run npm install