Solution :
This problem always shows up due to the version mismatch. To resolve this problem you need to do the following changes in the package.json file.
Step 1 : Go to your package.json and modify the "rxjs": "^6.0.0" to "rxjs": "6.0.0"
Step 2 : Now Run the npm update in your project.
Step 3 : If you are using the rxjs-compat then you must also need to do following in order to fixed your issue. Please change your rxjs-compat version from "rxjs-compat": "^6.2.2" to "rxjs-compat": "6.2.2"
Please note that there is no need to change the typescript version. I am currently using : "typescript": "~2.7.2"
OR
You just need to do some of the changes in your package.json
Go to your package.json and just modify "rxjs": "^6.0.0" to "rxjs": "6.0.0"
Then run the npm update in your project
OR
I had the same error while using the angular 6 having the rxjs@6.4.0 but I just downgraded it to the rxjs@6.3.3 and it worked.
Hope this will help in resolving your issue!
