Due to the existence of a version mismatch, such a problem could arise which to get past, will require certain changes in your package.json file. Follow the steps mentioned below:-
Start with Going to package.json and modify "rxjs": "^6.0.0" to "rxjs": "6.0.0"
Following which, run npm install in your project. I have been using the "typescript": "~2.7.2" version and there is no need to modify the typescript version. However, if you are using rxjs-compat then you also need to change the rxjs-compat version from "rxjs-compat": "^6.2.2" to "rxjs-compat": "6.2.2"
I hope this helps you solve your problem.
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