This error comes into picture in two scenario :
1. selenium-server-standalone-3.0.1.jar does not exist :
In your project's
"node_modules\protractor\node_modules\webdriver-manager\selenium"
location.
To Resolve this you have to run following command :
webdriver-manager update
2. selenium-server-standalone exists with different version :
In this scenario you have to download the required selenium-server-standalone jar as follow :
webdriver-manager update --versions.standalone "specific_version"
Example :
webdriver-manager update --versions.standalone 3.0.1
OR
node ./node_modules/protractor/bin/webdriver-manager update --versions.standalone 3.0.1